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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2018	Nov. 02, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Trading Symbol	FORR
Entity Registrant Name	FORRESTER RESEARCH, INC.
Entity Central Index Key	0001023313
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		18,264,000

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 92,057	$ 79,790
Marketable investments (Note 4)	52,395	54,333
Accounts receivable, net	38,552	70,023
Deferred commissions	10,884	13,731
Prepaid expenses and other current assets	13,292	18,942
Total current assets	207,180	236,819
Property and equipment, net	22,403	25,249
Goodwill	85,126	76,169
Intangible assets, net	5,368	732
Other assets	8,417	6,231
Total assets	328,494	345,200
Current Liabilities:
Accounts payable	512	217
Accrued expenses and other current liabilities	41,364	49,629
Deferred revenue	128,435	145,207
Total current liabilities	170,311	195,053
Non-current liabilities	11,353	8,958
Total liabilities	181,664	204,011
Stockholders' Equity (Note 9):
Preferred stock, $0.01 par value Authorized - 500 shares; issued and outstanding - none
Common stock, $0.01 par value Authorized - 125,000 shares Issued - 22,893 and 22,432 shares as of September 30, 2018 and December 31, 2017, respectively Outstanding - 18,262 and 18,041 shares as of September 30, 2018 and December 31, 2017, respectively	229	224
Additional paid-in capital	196,803	181,910
Retained earnings	126,006	123,010
Treasury stock - 4,631 and 4,391 shares as of September 30, 2018 and December 31, 2017, respectively, at cost	(171,889)	(161,943)
Accumulated other comprehensive loss	(4,319)	(2,012)
Total stockholders’ equity	146,830	141,189
Total liabilities and stockholders’ equity	$ 328,494	$ 345,200

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	500,000	500,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	22,893,000	22,432,000
Common stock, shares outstanding	18,262,000	18,041,000
Treasury stock, shares	4,631,000	4,391,000

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Total revenues	$ 84,890	$ 80,369	$ 258,992	$ 247,296
Operating expenses:
Selling and marketing	31,051	29,225	96,771	90,355
General and administrative	11,192	10,083	32,871	30,672
Depreciation	1,965	1,607	6,056	4,775
Amortization of intangible assets	402	197	770	582
Acquisition and integration costs	977		1,306
Total operating expenses	79,948	73,620	245,311	227,198
Income from operations	4,942	6,749	13,681	20,098
Other income, net	319	146	472	248
Losses on investments, net	(17)	(772)	(62)	(997)
Income before income taxes	5,244	6,123	14,091	19,349
Income tax expense	1,294	2,170	4,086	6,302
Net income	$ 3,950	$ 3,953	$ 10,005	$ 13,047
Basic income per common share	$ 0.22	$ 0.22	$ 0.55	$ 0.73
Diluted income per common share	$ 0.21	$ 0.22	$ 0.55	$ 0.72
Basic weighted average common shares outstanding	18,088	17,747	18,030	17,897
Diluted weighted average common shares outstanding	18,433	18,051	18,353	18,212
Cash dividends declared per common share	$ 0.20	$ 0.19	$ 0.60	$ 0.57
Research Services [Member]
Revenues:
Total revenues	$ 56,332	$ 54,235	$ 166,332	$ 160,553
Advisory Services and Events [Member]
Revenues:
Total revenues	28,558	26,134	92,660	86,743
Cost of Services and Fulfillment [Member]
Operating expenses:
Cost of services and fulfillment	$ 34,361	$ 32,508	$ 107,537	$ 100,814

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 3,950	$ 3,953	$ 10,005	$ 13,047
Other comprehensive income (loss), net of taxes:
Foreign currency translation	(602)	1,601	(2,293)	4,905
Net change in market value of investments	65	23	12	47
Other comprehensive income (loss)	(537)	1,624	(2,281)	4,952
Comprehensive income	$ 3,413	$ 5,577	$ 7,724	$ 17,999

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 10,005	$ 13,047
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	6,056	4,775
Amortization of intangible assets	770	582
Net losses from investments	62	997
Deferred income taxes	(1,305)	(921)
Stock-based compensation	6,191	6,423
Amortization of premium (discount) on investments	(17)	171
Foreign currency losses	462	444
Changes in assets and liabilities, net of acquisitions:
Accounts receivable	31,857	20,140
Deferred commissions	3,716	2,906
Prepaid expenses and other current assets	(68)	(979)
Accounts payable	19	(1,208)
Accrued expenses and other liabilities	(12,111)	(6,041)
Deferred revenue	(8,205)	(3,473)
Net cash provided by operating activities	37,432	36,863
Cash flows from investing activities:
Acquisitions, net of cash acquired	(9,250)
Purchases of property and equipment	(3,161)	(5,806)
Purchases of marketable investments	(31,831)	(27,430)
Proceeds from sales and maturities of marketable investments	33,802	34,458
Other investing activity		200
Net cash provided by (used in) investing activities	(10,440)	1,422
Cash flows from financing activities:
Dividends paid on common stock	(10,839)	(10,205)
Repurchases of common stock	(9,946)	(39,967)
Proceeds from issuance of common stock under employee equity incentive plans	11,217	13,866
Taxes paid related to net share settlements of stock-based compensation awards	(2,509)	(2,511)
Net cash used in financing activities	(12,077)	(38,817)
Effect of exchange rate changes on cash and cash equivalents	(2,648)	3,534
Net increase in cash and cash equivalents	12,267	3,002
Cash and cash equivalents, beginning of period	79,790	76,958
Cash and cash equivalents, end of period	92,057	79,960
Supplemental disclosure of cash flow information:
Cash paid for income taxes	$ 3,263	$ 7,662

Consolidated Statements of Cash Flows (Parenthetical) - FeedbackNow [Member] $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Non-cash investing activities, total consideration payable	$ 5.3
Non-cash investing activities, contingent consideration	3.0
Non-cash investing activities, indemnity holdback	1.5
Non-cash investing activities, working capital adjustment	$ 0.8

Interim Consolidated Financial Statements

9 Months Ended

Sep. 30, 2018

Accounting Policies [Abstract]

Interim Consolidated Financial Statements

Note 1 — Interim Consolidated Financial Statements

Basis of Presentation

The accompanying unaudited interim consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial information and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for reporting on Form 10-Q. Accordingly, certain information and footnote disclosures required for complete financial statements are not included herein. The year-end balance sheet data was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America. It is recommended that these financial statements be read in conjunction with the consolidated financial statements and related notes that appear in the Forrester Research, Inc. (“Forrester”) Annual Report on Form 10-K for the year ended December 31, 2017. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair statement of the financial position, results of operations, comprehensive income and cash flows as of the dates and for the periods presented have been included. The results of operations for the three and nine months ended September 30, 2018 may not be indicative of the results for the year ending December 31, 2018, or any other period.

Out of Period Adjustment

During the quarter ended June 30, 2018, the Company recorded $1.0 million of revenue ($0.7 million after tax) for an out-of-period correction within research services in the Consolidated Statements of Income. The error resulted from an understatement of revenue from the reprint product line of $0.8 million ($0.5 million after tax) during the three months ended March 31, 2018 and $0.2 million ($0.1 million after tax) from the year ended December 31, 2017. The Company has concluded that the error was not material to all prior period financial statements.

Fair Value Measurements

The carrying amounts reflected in the Consolidated Balance Sheets for cash and cash equivalents, accounts receivable, accounts payable, and accrued expenses approximate fair value due to their short-term maturities. See Note 2 – Acquisitions – for the fair value of a contingent consideration arrangement. See Note 4 – Marketable Investments - for the fair value of the Company’s marketable investments.

Adoption of New Accounting Pronouncements

The Company adopted the guidance in Accounting Standards Update (“ASU”) No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments, on January 1, 2018. The new standard clarifies certain aspects of the statement of cash flows, including contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, and distributions received from equity method investees, among others. The adoption of this standard did not have a material impact on the Company’s statements of cash flows.

The Company adopted the guidance in ASU No. 2016-18, Statement of Cash Flows: Restricted Cash, on January 1, 2018. The new standard requires restricted cash to be included with cash and cash equivalents when reconciling the beginning and ending amounts on the statement of cash flows. The adoption of this standard did not have an impact on the Company’s statements of cash flows.

The Company elected to adopt the guidance in ASU No. 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, on January 1, 2018. The new standard allows but does not require, a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act (the “Act”) enacted on December 22, 2017. The Company elected to make the reclassification adjustment as of the beginning of the period of adoption in the amount of $26,000 using the aggregate portfolio approach. The reclassification amount includes the effect of the change in the U.S. federal corporate income tax rate on the gross deferred tax amounts at the date of enactment of the Act related to items remaining in accumulated other comprehensive income.

In May 2014, the Financial Accounting Standards Board (FASB) issued ASU No. 2014-09, Revenue from Contracts with Customers, and has since issued several additional amendments thereto (collectively known as ASC 606). ASC 606 supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. ASC 606 also includes subtopic ASC 340-40, Other Assets and Deferred Costs-Contracts with Customers, which provides guidance on accounting for certain revenue related costs including costs associated with obtaining and fulfilling a contract.

On January 1, 2018, the Company adopted ASC 606 using the modified retrospective method. Under this method, the reported results for 2018 reflect the application of ASC 606, while the reported results for 2017 were prepared under the guidance of ASC 605, Revenue Recognition, which is referred to herein as the “previous guidance”. The modified retrospective method requires the cumulative effect of applying the new guidance to all contracts with customers that were not completed as of January 1, 2018 to be recorded as an adjustment to retained earnings as of the adoption date. Forrester considered a contract to be complete if all the revenue was recognized in accordance with the previous guidance that was in effect before the adoption date.

The effect of adopting ASC 606 included a $7.8 million reduction in deferred revenue, primarily related to prepaid performance obligations that are expected to expire in 2018 and 2019 that would have been recognized in 2017 under the new guidance; a decrease of $5.5 million in prepaid expenses and other current assets related to deferred survey costs that would have been expensed as incurred in 2017 under the new guidance and the current tax impact of the cumulative effect; an increase of $0.9 million in deferred commissions related to the capitalization of fringe benefits as incremental costs to obtain customer contracts under the new guidance; and an increase of $0.6 million in other assets for the deferred tax effect of the cumulative effect. Retained earnings increased by $3.8 million as a net result of these adjustments.

Refer to Note 6, Revenue and Contract Costs, for additional disclosures and a discussion of the Company's updated policies related to revenue recognition, related balance sheet accounts, and accounting for costs to obtain and fulfill a customer contract.

The following tables summarize the effect of adopting ASC 606 on the Company’s financial statements during and as of the three and nine months ended September 30, 2018 (in thousands):

Consolidated Balance Sheet
	As of September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Accounts receivable, net	$	38,552	$	41,837
Deferred commissions		10,884		10,284
Prepaid expenses and other current assets		13,292		17,966
Total current assets		207,180		214,539
Other assets		8,417		7,855
Total assets		328,494		335,291

Deferred revenue	$	128,435	$	138,060
Total current liabilities		170,311		179,936
Total liabilities		181,664		191,289
Retained earnings		126,006		123,178
Total stockholders’ equity		146,830		144,002
Total liabilities and stockholders’ equity		328,494		335,291

Total assets were $6.8 million less than if the previous guidance remained in effect, largely due to the following changes required by the adoption of ASC 606:

•

Accounts receivable, net was lower due to the Company excluding invoices issued on cancellable contracts in excess of revenue recognized.

•

Deferred commissions was higher due to the capitalization of fringe benefits costs.

•

Prepaid expenses and other current assets were lower due to expensing survey costs as incurred and the current period tax effect of the adjustments.

Deferred revenue was $9.6 million less due to the accelerated recognition of revenue for estimated unexercised rights, which would have been deferred under the previous guidance until the right expired, and the exclusion of invoices issued on cancellable contracts in excess of revenue recognized.

Consolidated Statement of Income
	Three Months Ended September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Revenues:
Research services	$	56,332	$	55,719
Advisory services and events		28,558		28,287
Total revenues		84,890		84,006
Operating expenses:
Cost of services and fulfillment		34,361		34,838
Selling and marketing		31,051		30,871
Total operating expenses		79,948		80,245
Income from operations		4,942		3,761
Income before income taxes		5,244		4,063
Income tax provision		1,294		927
Net income		3,950		3,136
Basic income per common share	$	0.22	$	0.17
Diluted income per common share	$	0.21	$	0.17

Consolidated Statement of Income
	Nine Months Ended September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Revenues:
Research services	$	166,332	$	167,429
Advisory services and events		92,660		93,051
Total revenues		258,992		260,480
Operating expenses:
Cost of services and fulfillment		107,537		107,841
Selling and marketing		96,771		96,502
Total operating expenses		245,311		245,346
Income from operations		13,681		15,134
Income before income taxes		14,091		15,544
Income tax provision		4,086		4,564
Net income		10,005		10,980
Basic income per common share	$	0.55	$	0.61
Diluted income per common share	$	0.55	$	0.60

The $0.9 million increase and $1.5 million reduction to total revenues for three and nine months ended September 30, 2018, respectively, is related to ASC 606’s requirement to recognize revenue for estimated future unexercised customer rights rather than recognize unexercised rights when they occur. The Company currently expects this change to primarily affect the timing of revenue within the quarters of 2018 but does not expect it to have a material effect on the Company’s results of operations for the full year of 2018. The net impact, including the tax effect, of accounting for revenue and costs to obtain and fulfill customer contracts under the new guidance increased net income and diluted net income per share for the three months ended September 30, 2018 by $0.8 million and $0.04, respectively. For the nine months ended September 30, 2018, the net impact of the new guidance decreased net income and diluted net income per share by $1.0 million and $0.05, respectively.

Consolidated Statement of Comprehensive Income
	Three Months Ended September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Net income	$	3,950	$	3,136
Comprehensive income		3,413		2,599

Consolidated Statement of Comprehensive Income
	Nine Months Ended September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Net income	$	10,005	$	10,980
Comprehensive income		7,724		8,698

Consolidated Statement of Cash Flows
	Nine Months Ended September 30, 2018
				Amounts as
				if Previous
				Guidance in
	As Reported			Effect
Cash flows from operating activities:
Net income	$	10,005		$	10,980
Accounts receivable		31,857			28,572
Deferred commissions		3,716			3,447
Prepaid expenses and other current assets		(68	)		714
Deferred revenue		(8,205	)		(6,408	)

The impact to comprehensive income and cash flows from operating activities are driven by the consolidated balance sheet and income statement changes previously discussed.

Acquisitions

9 Months Ended

Sep. 30, 2018

Business Combinations [Abstract]

Acquisitions

Note 2 — Acquisitions

The Company accounts for business combinations in accordance with the acquisition method of accounting as prescribed by ASC 805, Business Combinations. The acquisition method of accounting requires the Company to record the assets and liabilities acquired based on their estimated fair values as of the acquisition date, with any excess of the consideration transferred over the estimated fair value of the net assets acquired, including identifiable intangible assets, to be recorded to goodwill.

GlimpzIt

On June 22, 2018, Forrester acquired substantially all of the assets of SocialGlimpz Inc. (“GlimpzIt”), an artificial intelligence and machine-learning provider based in San Francisco. The acquisition is part of Forrester's plan to build a real-time customer experience or CX cloud solution, integrating a range of inputs to help companies monitor and improve customer experience. Forrester intends to deploy the GlimpzIt technology to extend the analytics engine in Forrester’s planned real-time CX cloud. The acquisition of GlimpzIt was determined to be an acquisition of a business under the provisions of ASC 805. The total purchase price was approximately $1.3 million, which was paid in cash on the acquisition date, and has been preliminarily allocated as $0.7 million of goodwill and $0.6 million of an intangible asset representing technology, which is being amortized over its estimated useful life of five years. The acquired working capital was insignificant. Forrester may also be required to pay an additional $0.3 million in cash contingent on the achievement of certain employment conditions by key employees, which is being recognized as compensation expense over the related service period of two years. Goodwill has been allocated to the Product segment and is expected to be deductible for income tax purposes. Goodwill is attributable to the acquired workforce as well as future synergies. The results of GlimpzIt operations were not material to our consolidated results of operations, and accordingly, no pro forma financial information has been presented.

FeedbackNow

On July 6, 2018, Forrester acquired 100% of the shares of S.NOW SA, a Switzerland-based business that operates as FeedbackNow. FeedbackNow is a maker of physical buttons and monitoring software that companies deploy to measure, analyze, and improve customer experience. The acquisition is part of Forrester's plan to build a real-time CX cloud solution. FeedbackNow provides a high-volume input source for the real-time CX cloud solution. The acquisition of FeedbackNow was determined to be an acquisition of a business under the provisions of ASC 805. The Company paid $8.4 million on the closing date. An additional $1.5 million is payable during a two-year period from the closing date and is subject to typical indemnity provisions from the seller. The Company is also required to pay additional purchase price based on the acquired working capital of $0.8 million and the sellers may earn up to $4.2 million based on the financial performance of FeedbackNow during the two-year period following the closing date.

Total Consideration Transferred

The following table summarizes the fair value of the aggregate consideration paid or payable for FeedbackNow (in thousands):


Cash paid at close (1)	$	8,425
Working capital adjustment (2)		798
Indemnity holdback (3)		1,485
Contingent purchase price (4)		3,015
Total	$	13,723

(1)

The cash paid at close represents the gross contractual amount paid. Net cash paid, which accounts for the cash acquired of $0.5 million, was $8.0 million and is reflected as an investing activity in the Consolidated Statements of Cash Flows.

(2)

Amount represents the provisional amount payable to the sellers based upon working capital as defined. This amount is subject to adjustment and the Company expects to pay the working capital adjustment by the end of 2018.

(3)

Approximately $0.5 million and $1.0 million of the holdback is expected to be paid during 2019 and 2020, respectively.

(4)

The acquisition of FeedbackNow includes a contingent consideration arrangement that requires additional consideration to be paid to the sellers based on the financial performance of FeedbackNow during the two-year period subsequent to the closing date. Up to $1.7 million and $2.5 million could be payable during 2019 and 2020, respectively, if the financial targets are met. The range of undiscounted amounts that could be payable under this arrangement is zero to $4.2 million. The fair value of the contingent consideration recognized on the acquisition date, which represents purchase price, is $3.0 million. The fair value was estimated by applying a simulation valuation approach. That measure is based on significant Level 3 inputs not observable in the market. Key assumptions include projected financial results and the discount rate used. As of September 30, 2018, the change in the recognized amounts for the contingent consideration was immaterial and there was no change to the range of outcomes.

Preliminary Allocation of Purchase Price

The following table summarizes the preliminary allocation of the purchase price to the fair value of the assets acquired and liabilities assumed for the acquisition of FeedbackNow (in thousands):


Assets:
Cash	$	463
Accounts receivable		846
Prepaids and other current assets		465
Goodwill (1)		9,087
Acquired intangible assets (2)		4,780
Other assets		75
Total assets		15,716
Liabilities:
Accounts payable and accrued liabilities		908
Contract liabilities		260
Deferred tax liability		825
Total liabilities		1,993
Net assets acquired	$	13,723

(1) Goodwill represents the expected synergies from combining FeedbackNow with Forrester as well as the value of the acquired workforce.

(2) All of the acquired intangible assets are finite-lived. The determination of the fair value of the finite-lived intangible assets required management judgment and the consideration of a number of factors. In determining the fair values, management primarily relied on income valuation methodologies, in particular discounted cash flow models. The use of discounted cash flow models required the use of estimates, including projected cash flows related to the particular asset; the useful lives of the particular assets; the selection of royalty and discount rates used in the models; and certain published industry benchmark data. In establishing the estimated useful lives of the acquired intangible assets, the Company relied primarily on the duration of the cash flows utilized in the valuation model. Of the $4.8 million assigned to acquired intangible assets, $3.0 million was assigned to the technology asset class with a useful of 6.5 years, $1.3 million to customer relationships with a useful life of 4.5 years, and $0.5 million to trade names with a useful life of 8.5 years. Amortization of acquired intangible assets was $0.2 million for both the three and nine months ended September 30, 2018.

The allocation of the purchase price for FeedbackNow is preliminary with respect to the valuation of acquired intangible assets, contingent purchase price, working capital and goodwill. The Company expects to obtain the remainder of the information to complete the allocation of purchase price by the end of 2018.

The Company's financial statements include the operating results of FeedbackNow beginning on July 6, 2018, the date of acquisition. FeedbackNow's operating results and the related goodwill are being reported as part of the Company's Product segment. The goodwill is not deductible for income tax purposes. The acquisition of FeedbackNow added approximately $0.5 million and $1.1 million of revenue and direct expenses, respectively, in the three months ended September 30, 2018. The results of FeedbackNow operations were not material to our consolidated results of operations for prior periods, and accordingly, no prior period pro forma information has been presented.

In the nine months ended September 30, 2018, goodwill increased by $9.0 million with $9.8 million of the increase attributable to the acquisitions of GlimpzIt and FeedbackNow and a $0.8 million decrease due to foreign currency fluctuations.

The Company recognized $0.1 million and $0.4 million of acquisition costs in the three and nine months ended September 30, 2018, respectively. The costs primarily consisted of legal fees and accounting and tax professional fees.

Accumulated Other Comprehensive Loss

9 Months Ended

Sep. 30, 2018

Equity [Abstract]

Accumulated Other Comprehensive Loss

Note 3 — Accumulated Other Comprehensive Loss

The components of accumulated other comprehensive loss are as follows (in thousands):

							Total
	Net Unrealized			Cumulative			Accumulated
	Loss on Marketable			Translation			Other Comprehensive
	Investments			Adjustment			Loss
Balance at January 1, 2018	$	(115	)	$	(1,897	)	$	(2,012	)
Reclassification of stranded tax effects from tax reform		(26	)		—			(26	)
Foreign currency translation		—			(2,293	)		(2,293	)
Unrealized gain on investments, net of tax of $4		12			—			12
Balance at September 30, 2018	$	(129	)	$	(4,190	)	$	(4,319	)

							Total
	Net Unrealized			Cumulative			Accumulated
	Loss on Marketable			Translation			Other Comprehensive
	Investments			Adjustment			Loss
Balance at January 1, 2017	$	(83	)	$	(7,490	)	$	(7,573	)
Foreign currency translation		—			4,905			4,905
Unrealized gain on investments, net of tax of $29		47			—			47
Balance at September 30, 2017	$	(36	)	$	(2,585	)	$	(2,621	)

							Total
	Net Unrealized			Cumulative			Accumulated
	Loss on Marketable			Translation			Other Comprehensive
	Investments			Adjustment			Loss
Balance at July 1, 2018	$	(194	)	$	(3,588	)	$	(3,782	)
Foreign currency translation		—			(602	)		(602	)
Unrealized gain on investments, net of tax of $21		65			—			65
Balance at September 30, 2018	$	(129	)	$	(4,190	)	$	(4,319	)

							Total
	Net Unrealized			Cumulative			Accumulated
	Loss on Marketable			Translation			Other Comprehensive
	Investments			Adjustment			Loss
Balance at July 1, 2017	$	(59	)	$	(4,186	)	$	(4,245	)
Foreign currency translation		—			1,601			1,601
Unrealized gain on investments, net of tax of $14		23			—			23
Balance at September 30, 2017	$	(36	)	$	(2,585	)	$	(2,621	)

Marketable Investments

9 Months Ended

Sep. 30, 2018

Investments Debt And Equity Securities [Abstract]

Marketable Investments

Note 4 — Marketable Investments

The following table summarizes the Company’s marketable investments (in thousands):

	As of September 30, 2018
			Gross		Gross
	Amortized		Unrealized		Unrealized			Market
	Cost		Gains		Losses			Value
Corporate obligations	$	52,567	$	1	$	(173	)	$	52,395

	As of December 31, 2017
			Gross		Gross
	Amortized		Unrealized		Unrealized			Market
	Cost		Gains		Losses			Value
Federal agency obligations	$	1,800	$	—	$	(7	)	$	1,793
Corporate obligations		52,721		—		(181	)		52,540
Total	$	54,521	$	—	$	(188	)	$	54,333

Realized gains and losses on investments are included in earnings and are determined using the specific identification method. Realized gains and losses on the sale of the Company’s marketable investments were not material in the three and nine months ended September 30, 2018 and 2017.

The following table summarizes the maturity periods of the marketable investments in the Company’s portfolio as of September 30, 2018 (in thousands).

		FY 2018				FY 2019				FY2020				Total
Corporate obligations		$	19,786			$	26,833			$	5,776			$	52,395

The following table shows the gross unrealized losses and market value of the Company’s available-for-sale securities with unrealized losses that are not deemed to be other-than-temporary, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position (in thousands):

	As of September 30, 2018
	Less Than 12 Months				12 Months or Greater
	Market		Unrealized		Market		Unrealized
	Value		Losses		Value		Losses
Corporate obligations	$	26,181	$	32	$	24,202	$	141

	As of December 31, 2017
	Less Than 12 Months				12 Months or Greater
	Market		Unrealized		Market		Unrealized
	Value		Losses		Value		Losses
Federal agency obligations	$	—	$	—	$	1,793	$	7
Corporate obligations		31,723		149		20,817		32
Total	$	31,723	$	149	$	22,610	$	39

Fair Value

The Company measures certain financial assets at fair value on a recurring basis, including cash equivalents and available-for-sale securities. The fair values of these financial assets have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements.

Level 1 — Fair value based on quoted prices in active markets for identical assets or liabilities.

Level 2 — Fair value based on inputs other than Level 1 inputs that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 — Fair value based on unobservable inputs that are supported by little or no market activity and such inputs are significant to the fair value of the assets or liabilities.

The following table represents the Company’s fair value hierarchy for its financial assets (cash equivalents and investments) measured at fair value on a recurring basis (in thousands):

	As of September 30, 2018
	Level 1		Level 2		Level 3		Total
Money market funds (1)	$	2,952	$	—	$	—	$	2,952
Corporate obligations		—		52,395		—		52,395
Total	$	2,952	$	52,395	$	—	$	55,347

	As of December 31, 2017
	Level 1		Level 2		Level 3		Total
Money market funds (1)	$	492	$	—	$	—	$	492
Federal agency obligations		—		1,793		—		1,793
Corporate obligations		—		52,540		—		52,540
Total	$	492	$	54,333	$	—	$	54,825

(1)	Included in cash and cash equivalents.

Level 2 assets consist of the Company’s entire portfolio of marketable investments. Level 2 assets have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, typically utilizing third party pricing services or other market observable data. The pricing services utilize industry standard valuation methods, including both income and market based approaches and observable market inputs to determine value. These observable market inputs include reportable trades, benchmark yields, credit spreads, broker/dealer quotes, bids, offers, current spot rates and other industry and economic events.

Refer to Note 2 – Acquisitions for the Company’s discussion on the fair value measurement of the FeedbackNow contingent purchase price, which is a Level 3 financial liability.

Non-Marketable Investments	9 Months Ended
Non-Marketable Investments	Sep. 30, 2018
Investments Debt And Equity Securities [Abstract]
Non-Marketable Investments	Note 5 — Non-Marketable Investments At September 30, 2018 and December 31, 2017, the carrying value of the Company’s non-marketable investments, which were composed of interests in technology-related private equity funds, was $1.8 million and $1.9 million, respectively, and is included in other assets in the Consolidated Balance Sheets. The Company’s investments at September 30, 2018 are being accounted for using the equity method as the investments are limited partnerships and the Company has an ownership interest in excess of 5% and, accordingly, the Company records its share of the investee’s operating results each period. Losses from non-marketable investments were $0.1 million during the nine months ended September 30, 2018 and were immaterial during the three months ended September 30, 2018. Losses were $0.8 million and $1.0 million during the three and nine months ended September 30, 2017, respectively. Losses are included in losses on investments, net in the Consolidated Statements of Income. During the three and nine months ended September 30, 2018, no distributions were received from the funds. During the three months ended September 30, 2017, no distributions were received from the funds. During the nine months ended September 30, 2017, $0.4 million of distributions were received from the funds.

Revenue and Contract Costs	9 Months Ended
Revenue and Contract Costs	Sep. 30, 2018
Revenue From Contract With Customer [Abstract]
Revenue and Contract Costs	Note 6 – Revenue and Contract Costs Revenue Policy The Company adopted ASC 606 on January 1, 2018 using the modified retrospective approach, which applies to all contracts not complete as of the date of adoption. Under ASC 606, the Company recognizes revenue when a customer obtains control of promised goods or services, in an amount that reflects the consideration expected to be received in exchange for those goods or services. The Company follows the five step model prescribed under ASC 606: (i) identify contract(s) with a customer; (ii) identify the performance obligation(s) in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies the performance obligation. Revenues are presented net of any sales or value added taxes collected from customers and remitted to the government. The Company accounts for a contract when it has approval and commitment from both parties, the rights of the parties are identified, payment terms are identified, the contract has commercial substance and collectability of consideration expected to be transferred to the customer is probable. The Company applies judgment in determining the customer’s ability and intention to pay for services expected to be transferred, which is based on factors including the customer’s payment history, management’s ability to mitigate exposure to credit risk (for example, requiring payment in advance of the transfer of goods or services, or the ability to stop transferring promised goods or services in the event a customer fails to pay consideration when due) and experience selling to similarly situated customers. Performance obligations within a contract are identified based on the goods and services promised to be transferred in the contract. When a contract includes more than one promised good or service, the Company must apply judgment to determine whether the promises represent multiple performance obligations or a single, combined performance obligation. This evaluation requires the Company to determine if the promises are both capable of being distinct, where the customer can benefit from the good or service on its own or together with other resources readily available, and are distinct within the context of the contract, where the transfer of goods or services is separately identifiable from other promises in the contract. When both criteria are met, each promised good or service is accounted for as a separate performance obligation. In cases where the promises are distinct, the Company is further required to evaluate if the promises are a series of goods and services that are substantially the same and have the same pattern of transfer to the customer (referred to as the “series” guidance). When the Company determines that promises meet the series guidance, they are accounted for as a single, combined performance obligation. The number of performance obligations in the Company’s arrangements is not different under ASC 606 than the number of separate units of accounting under pervious guidance, as discussed further below. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation on a relative basis according to their standalone selling prices. The Company continues to determine standalone selling price based on the price at which the performance obligation is sold separately. If the Company does not have a history of selling a performance obligation, management applies judgment to estimate the standalone selling price, taking into consideration available information, including market conditions, factors considered to set list price, pricing of similar products, and internal pricing objectives. The corresponding allocated revenues are recognized as the performance obligations are satisfied, as discussed below. Research services revenues Research services revenues consist primarily of memberships to Research, Connect, and Analytics products. The majority of the Research revenues are annual subscriptions to our research, including access to all or a designated portion of our research and, depending on the type of license, unlimited phone or email analyst inquiry and unlimited participation in Forrester webinars, all of which are delivered throughout the contract period. The Company has concluded that the promises represent a stand ready obligation to provide a daily information service, in which the services are the same each day, every day is distinct, and the customer simultaneously receives and consumes the benefits as the Company transfers control throughout the contract period. Accordingly, these subscriptions meet the requirements of the series guidance and are each accounted for as a single performance obligation. The Company recognizes revenue ratably over time, using an output measure of time elapsed. Research revenues also include sales of electronic reprints, which are written research documents prepared by Forrester’s analysts and hosted via an on-line platform. Reprints include a promise to deliver a customer-selected research document and certain usage data provided through the on-line platform, which represents two performance obligations. The Company satisfies the performance obligation for the research document by providing access to the electronic reprint and accordingly recognizes revenue at that point in time. The Company satisfies the performance obligation for the data portion of the reprint on a daily basis and accordingly recognizes revenue over time. The majority of the Connect revenues are the Company’s Leadership Board product which includes access to the Research offering, access to a private forum with other Leadership Board member peers, access to a Forrester advisor, member-generated content, and one Event ticket. The Company has concluded that all promises, other than the Event ticket, represent a stand ready obligation to provide a daily information and peer service, in which the services are the same each day, every day is distinct, and the customer simultaneously receives and consumes the benefits as the Company transfers control throughout the contract period. Accordingly, these promises meet the requirements of the series guidance and are accounted for as a single performance obligation. The Company recognizes revenue ratably over time, using an output measure of time elapsed. The Event ticket is accounted for as a separate performance obligation and is recognized when the Event occurs. Analytics revenues are annual subscriptions to access designated survey data products and typically include a data advisor, all of which are delivered throughout the contract period. For Analytics subscriptions, the Company has concluded that the promises represent a stand ready obligation to provide a daily data service, in which the services are the same each day, every day is distinct, and the customer simultaneously receives and consumes the benefits as the Company transfers control throughout the contract period. Accordingly, these subscriptions meet the requirements of the series guidance and are accounted for as a single performance obligation. The Company recognizes revenue ratably over time, using an output measure of time elapsed. Certain of the Analytics products include advisory services which are accounted for as a separate performance obligation and are recognized at the point in time the session is completed or the final deliverable is transferred to the customer. Advisory services and events revenues Advisory services and events revenues consists of sales of advisory services, consulting projects, and Events. Advisory services revenues are short-term presentations or knowledge sharing sessions (which can range from one hour to two days), such as workshops, speeches and advisory days. Each is a promise for a Forrester analyst to deliver a deeper understanding of Forrester’s published research and represents a single performance obligation. Revenue is recognized at the point in time the session is completed or the final deliverable is transferred to the customer. Consulting project revenues consists of the delivery of focused insights and recommendations that assist customers with their challenges in developing and executing strategies around technology, customer experience and digital transformation. Projects are fixed-fee arrangements that are generally completed within two weeks to three months. The Company concluded that each project represents a single performance obligation as they are a single promise to deliver a customized engagement and deliverable. For the majority of these services, either practically or contractually, the work performed and delivered to the customer has no alternative use to the Company. Additionally, Forrester maintains an enforceable right to payment at all times throughout the contract. The Company utilizes an input method and recognizes revenue over time, based on hours expended relative to the total estimated hours required to satisfy the performance obligation. This input method was chosen since it closely aligns with how control of interim deliverables is transferred to the customer throughout the engagement and is also the method used internally to price the project and assess operational performance. If the Company were to enter into an agreement where it does not have an enforceable right to payment at all times, revenue would be recognized at the point in time the project is completed. Events revenues consist of either ticket or sponsorship sales for a Forrester-hosted event. Each is a single promise that either allows entry to, or grants the right to, promote a product or service at, a specific event. The Company concluded that each of these represents a single performance obligation. The Company recognizes revenue at the completion of the Event, which is the point in time when the customer has received the benefit(s) from attending or sponsoring the Event. Prepaid performance obligations, including Event tickets, reprints, advisory and consulting hours, on non-cancellable contracts that the Company estimates will expire unused are recognized in proportion to the pattern of related rights exercised by the customer. This assessment requires significant judgment, including estimating the percentage of prepaid rights that will go unexercised and anticipating the impact that future changes to products, pricing and customer engagement will have on actual expirations. The Company periodically updates the rates used to recognize unexercised rights. Refer to Note 10, Operating Segments, for a summary of disaggregated revenue by product category and business segment. Contract Modifications The Company considers a contract modification to exist when a mutually agreed upon change creates new, or updates existing, enforceable rights and obligations. ASC 606 introduced three specific methods to account for contract modifications depending on the nature of the change(s) in scope or price to the original contract. The new guidance is consistent with how the Company has historically accounted for contract modifications and as a result, does not have an impact on the Company’s results of operations. The majority of the Company’s contract modifications result in additional or remaining distinct goods and services and are treated on a prospective basis. Under the prospective method, the transaction price is updated to combine the unrecognized amount as of the modification date plus the additional transaction price from the modification. This amount is then re-allocated to the remaining distinct performance obligations and recognized accordingly. Consulting services contracts can be modified to update the scope of the services purchased. Since a consulting project is a single performance obligation that is only partially satisfied at the modification date, the updated project requirements are not distinct and the modification is accounted for as part of the existing contract. The effect of the modification on the transaction price and the Company’s measure of progress for the performance obligation to which is relates, is recognized as an adjustment to revenue (either an increase or decrease) on a cumulative catch-up basis. For the three and nine months ended September 30, 2018, the Company recorded an immaterial amount of cumulative catch-up adjustments. Accounts Receivable Accounts receivable includes amounts billed and currently due from customers. Since the only condition for payment of our invoices is the passage of time, the Company records a receivable on the date the invoice is issued. Also included in accounts receivable are unbilled amounts resulting from revenue exceeding the amount billed to the customer, where the right to payment is unconditional. If the right to payment for services performed was conditional on something other than the passage of time, the unbilled amount would be recorded as a separate contract asset. There were no contract assets as of September 30, 2018. The majority of the Company’s contracts are non-cancellable. However, for contracts that are cancellable by the customer, the Company does not record a receivable when it issues an invoice. The Company records accounts receivable on these contracts only up to the amount of revenue earned but not yet collected. In addition, since the majority of the Company’s contracts are for a duration of one year and payment is expected within one year from the transfer of goods and services, the Company does not adjust its receivables or transaction price for the effects of a significant financing component. Deferred Revenue The Company refers to contract liabilities as deferred revenue on the Consolidated Balance Sheets. Deferred revenue consists of billings in excess of revenue recognized. Similar to accounts receivable, the Company does not record deferred revenue for invoices issued on a cancellable contract. During the three and nine months ended September 30, 2018, the Company recognized approximately $24.7 million and $128.6 million of revenue related to its deferred revenue balance at January 1, 2018. To determine revenue recognized in the current period from deferred revenue at the beginning of the period, the Company first allocates revenue to the individual deferred revenue balance outstanding at the beginning of the period, until the revenue equals that balance. Approximately $251.2 million of revenue is expected to be recognized during the next 12 to 24 months from remaining performance obligations as of September 30, 2018. Cost to Obtain and Fulfill Contracts The Company capitalizes commissions paid to internal sales representatives and related fringe benefits costs that are incremental to obtaining customer contracts. These costs are included in deferred commissions on the Consolidated Balance Sheets. The judgments made in determining the amount of costs incurred include the types of costs to capitalize and whether the costs are in fact incremental. The Company elected the practical expedient to account for these costs at a portfolio level as the Company’s contracts are similar in nature and the amortization model used closely matches the amortization expense that would be recognized on a contract-by-contract basis. Costs to obtain a contract are amortized to operations as the related revenue is recognized over the initial contract term. Amortization expense related to deferred commissions was $7.2 million and $22.4 million for the three and nine months ended September 30, 2018, respectively. The Company evaluates the recoverability of deferred commissions at each balance sheet date. Costs to fulfill the Company’s contracts, such as our survey costs for our Analytics product line, do not meet the specified capitalization criteria as defined in the guidance and as such are expensed as incurred.

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Note 7 — Income Taxes Forrester provides for income taxes on an interim basis according to management’s estimate of the effective tax rate expected to be applicable for the full fiscal year. Certain items such as changes in tax rates, tax benefits or expense related to settlements of share-based payment awards, and foreign currency gains or losses are treated as discrete items and are recorded in the period in which they arise. Income tax expense for the nine months ended September 30, 2018 was $4.1 million resulting in an effective tax rate of 29.0% for the period. Income tax expense for the nine months ended September 30, 2017 was $6.3 million resulting in an effective tax rate of 32.6% for the period. Income tax expense decreased by $2.2 million during the nine months ended September 30, 2018 compared to the prior year period primarily due to a decrease in income before taxes for the 2018 period and a reduction in the federal tax rate due to the Tax Cuts and Jobs Act. These decreases were partially offset by a $1.3 million tax benefit recognized in the 2017 period from the settlement of a tax audit that did not recur in 2018. For the full year 2018, the Company anticipates that its effective tax rate will be approximately 31%. On December 22, 2017, the Tax Cuts and Jobs Act (the “Act”) was signed into law making significant changes to the Internal Revenue Code. The Company calculated its best estimate of the impact of the Act in its prior year end income tax provision in accordance with its understanding of the Act and guidance available at that date. On December 22, 2017, Staff Accounting Bulletin No. 118 ("SAB 118") was issued to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Act. SAB 118 provides a measurement period that should not extend beyond one year from the enactment date of the Act for companies to complete the accounting for the income tax effects of the Act. Any subsequent adjustment to these provisional amounts will be recorded to current tax expense in the quarter of 2018 when the analysis is complete. An immaterial adjustment to the provisional amount was recognized during the nine months ended September 30, 2018. In July 2015, the U.S. Tax Court issued an opinion in Altera Corp. v. Commissioner related to the treatment of stock-based compensation expense in an intercompany cost-sharing arrangement. The opinion invalidated part of a treasury regulation requiring stock-based compensation to be included in any qualified intercompany cost-sharing arrangement. The Company previously recorded a tax benefit based on the opinion in the case. Currently the U.S. Court of Appeals for the Ninth Circuit is reviewing the case and a final decision is yet to be issued. The Company will continue to monitor ongoing developments and potential impacts to its consolidated financial statements.

Net Income Per Common Share

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Net Income Per Common Share

Note 8 — Net Income Per Common Share

Basic net income per common share is computed by dividing net income by the basic weighted average number of common shares outstanding during the period. Diluted net income per common share is computed by dividing net income by the diluted weighted average number of common shares and common equivalent shares outstanding during the period. The weighted average number of common equivalent shares outstanding has been determined in accordance with the treasury-stock method. Common equivalent shares consist of common stock issuable on the exercise of outstanding stock options and the vesting of restricted stock units.

Basic and diluted weighted average common shares are as follows (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Basic weighted average common shares outstanding		18,088		17,747		18,030		17,897
Weighted average common equivalent shares		345		304		323		315
Diluted weighted average common shares outstanding		18,433		18,051		18,353		18,212
Options excluded from diluted weighted average share calculation as effect would have been anti-dilutive		1		27		10		177

Stockholders' Equity

9 Months Ended

Sep. 30, 2018

Equity [Abstract]

Stockholders' Equity

Note 9 — Stockholders’ Equity

Equity Plans

Restricted stock unit activity for the nine months ended September 30, 2018 is presented below (in thousands, except per share data):

				Weighted-
				Average
	Number of			Grant Date
	Shares			Fair Value
Unvested at December 31, 2017		509		$	37.59
Granted		245			44.01
Vested		(193	)		36.99
Forfeited		(35	)		37.20
Unvested at September 30, 2018		526		$	40.83

Stock option activity for the nine months ended September 30, 2018 is presented below (in thousands, except per share data and contractual term):

				Weighted -		Weighted -
				Average		Average
				Exercise		Remaining		Aggregate
	Number			Price Per		Contractual		Intrinsic
	of Shares			Share		Term (in years)		Value
Outstanding at December 31, 2017		937		$	35.10
Granted		—			—
Exercised		(267	)		34.92
Forfeited		(24	)		35.39
Outstanding at September 30, 2018		646		$	35.17		5.27	$	6,936
Exercisable at September 30, 2018		538		$	35.31		4.92	$	5,702
Vested and expected to vest at September 30, 2018		646		$	35.17		5.27	$	6,936

In May 2018, stockholders of the Company approved an amendment to the Company’s Amended and Restated Employee Stock Purchase Plan, which provided for an additional 400,000 shares of common stock, par value $0.01 per share, to be granted under the plan.

Stock-Based Compensation

Forrester recognizes the fair value of stock-based compensation in net income over the requisite service period of the individual grantee, which generally equals the vesting period. Stock-based compensation was recorded in the following expense categories (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Cost of services and fulfillment	$	1,001	$	1,088	$	3,128	$	3,387
Selling and marketing		261		170		752		535
General and administrative		858		920		2,311		2,501
Total	$	2,120	$	2,178	$	6,191	$	6,423

Forrester utilizes the Black-Scholes valuation model for estimating the fair value of shares subject to purchase under the employee stock purchase plan, which were valued using the following assumptions:

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2018			2017			2018			2017
Average risk-free interest rate		2.34	%		0.96	%		1.80	%		0.81	%
Expected dividend yield		1.6	%		1.9	%		1.9	%		1.9	%
Expected life	0.5 Years			0.5 Years			0.5 Years			0.5 Years
Expected volatility		25	%		26	%		22	%		24	%
Weighted average fair value	$	10.87		$	8.50		$	8.72		$	8.32

Dividends

In the nine months ended September 30, 2018, the Company declared and paid dividends of $10.8 million consisting of a $0.20 per share dividend in each of the first three quarters of 2018. In the nine months ended September 30, 2017, the Company declared and paid dividends of $10.2 million consisting of a $0.19 per share dividend in each of the first three quarters of 2017. In October 2018, the Company declared a dividend of $0.20 per share payable on December 26, 2018 to shareholders of record as of December 12, 2018.

Treasury Stock

As of September 30, 2018, Forrester’s Board of Directors had authorized an aggregate $535.0 million to purchase common stock under its stock repurchase program including $50.0 million authorized in February 2018. The shares repurchased may be used, among other things, in connection with Forrester’s equity incentive and purchase plans. In the three months ended September 30, 2018, the Company repurchased an insignificant number of shares at an aggregate cost of approximately $0.3 million. In the nine months ended September 30, 2018, the Company repurchased approximately 0.2 million shares of common stock at an aggregate cost of approximately $10.0 million. In the three and nine months ended September 30, 2017, the Company repurchased approximately 0.1 and 1.1 million shares, respectively, of common stock at an aggregate cost of approximately $3.5 and $40.0 million, respectively. From the inception of the program through September 30, 2018, the Company repurchased 16.3 million shares of common stock at an aggregate cost of $474.9 million.

Operating Segments

9 Months Ended

Sep. 30, 2018

Segment Reporting [Abstract]

Operating Segments

Note 10 — Operating Segments

The Product segment includes the costs of the product management organization that is responsible for product pricing and packaging and the launch of new products. In addition, this segment includes the costs of the Company’s Analytics, Connect and Events organizations. Revenue in this segment includes all revenue for the Company (including Research and Connect) except for revenue from advisory services and project consulting services that are delivered by personnel in the Research and Project Consulting segments.

The Research segment includes the costs of the Company’s research personnel who are responsible for writing the research and performing the webinars and inquiries for the Company’s Research and Connect products. In addition, the research personnel deliver advisory services (such as workshops, speeches and advisory days) and a portion of the Company’s project consulting services. Revenue in this segment includes only revenue from advisory services and project consulting services that are delivered by the research personnel in this segment.

The Project Consulting segment includes the costs of the consultants that deliver the majority of the Company’s project consulting services. Revenue in this segment includes the project consulting revenue delivered by the consultants in this segment.

The Company evaluates reportable segment performance and allocates resources based on segment revenues and expenses. Segment expenses include the direct expenses of each segment organization and exclude selling and marketing expenses, general and administrative expenses, stock-based compensation expense, depreciation expense, adjustments to incentive bonus compensation from target amounts, amortization of intangible assets, other income and losses on investments. The accounting policies used by the segments are the same as those used in the consolidated financial statements.

The Company is providing disaggregated revenue by product in the segment tables below in accordance with the revenue standard adopted on January 1, 2018.

						Project
	Product		Research			Consulting		Consolidated
Three Months Ended September 30, 2018
Research services revenues
Research	$	38,309	$	—		$	—	$	38,309
Connect		12,780		—			—		12,780
Analytics		5,243		—			—		5,243
Total research services revenues		56,332		—			—		56,332

Advisory services and events revenues
Advisory services		—		9,171			154		9,325
Consulting services		2,030		2,517			13,771		18,318
Events		915		—			—		915
Total advisory services and events revenues		2,945		11,688			13,925		28,558
Total segment revenues		59,277		11,688			13,925		84,890
Segment expenses		11,521		12,688			7,012		31,221
Contribution margin (loss)		47,756		(1,000	)		6,913		53,669
Selling, marketing, administrative and other expenses									(47,348	)
Amortization of intangible assets									(402	)
Acquisition and integration cost									(977	)
Other income and losses on investments									302
Income before income taxes								$	5,244

						Project
	Product		Research			Consulting		Consolidated
Three Months Ended September 30, 2017
Research services revenues
Research	$	36,894	$	—		$	—	$	36,894
Connect		12,506		—			—		12,506
Analytics		4,835		—			—		4,835
Total research services revenues		54,235		—			—		54,235

Advisory services and events revenues
Advisory services		—		8,297			81		8,378
Consulting services		2,250		2,082			12,321		16,653
Events		1,103		—			—		1,103
Total advisory services and events revenues		3,353		10,379			12,402		26,134
Total segment revenues		57,588		10,379			12,402		80,369
Segment expenses		9,764		11,953			6,443		28,160
Contribution margin (loss)		47,824		(1,574	)		5,959		52,209
Selling, marketing, administrative and other expenses									(45,263	)
Amortization of intangible assets									(197	)
Acquisition and integration cost									—
Other income and losses on investments									(626	)
Income before income taxes								$	6,123

						Project
	Product		Research			Consulting		Consolidated
Nine Months Ended September 30, 2018
Research services revenues
Research	$	114,007	$	—		$	—	$	114,007
Connect		37,882		—			—		37,882
Analytics		14,443		—			—		14,443
Total research services revenues		166,332		—			—		166,332

Advisory services and events revenues
Advisory services		—		29,664			290		29,954
Consulting services		6,079		7,306			40,397		53,782
Events		8,924		—			—		8,924
Total advisory services and events revenues		15,003		36,970			40,687		92,660
Total segment revenues		181,335		36,970			40,687		258,992
Segment expenses		36,534		38,182			20,930		95,646
Contribution margin (loss)		144,801		(1,212	)		19,757		163,346
Selling, marketing, administrative and other expenses									(147,589	)
Amortization of intangible assets									(770	)
Acquisition and integration cost									(1,306	)
Other income and losses on investments									410
Income before income taxes								$	14,091

						Project
	Products		Research			Consulting		Consolidated
Nine Months Ended September 30, 2017
Research services revenues
Research	$	110,550	$	—		$	—	$	110,550
Connect		36,103		—			—		36,103
Analytics		13,900		—			—		13,900
Total research services revenues		160,553		—			—		160,553

Advisory services and events revenues
Advisory services		—		25,889			254		26,143
Consulting services		7,495		6,390			38,496		52,381
Events		8,219		—			—		8,219
Total advisory services and events revenues		15,714		32,279			38,750		86,743
Total segment revenues		176,267		32,279			38,750		247,296
Segment expenses		32,788		36,510			18,886		88,184
Contribution margin (loss)		143,479		(4,231	)		19,864		159,112
Selling, marketing, administrative and other expenses									(138,432	)
Amortization of intangible assets									(582	)
Acquisition and integration cost									—
Other income and losses on investments									(749	)
Income before income taxes								$	19,349

Recent Accounting Pronouncements	9 Months Ended
Recent Accounting Pronouncements	Sep. 30, 2018
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
Recent Accounting Pronouncements	Note 11 — Recent Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases. The new standard requires that all lessees recognize the assets and liabilities that arise from leases on the balance sheet and disclose qualitative and quantitative information about its leasing arrangements. The new standard will be effective for the Company on January 1, 2019 and the Company has elected to adopt the standard under a modified retrospective method, in which case the cumulative effect of adopting the standard will be recorded as of January 1, 2019. We are currently evaluating the potential changes from this ASU to our future financial reporting and disclosures and designing and implementing related processes and controls. The adoption of this standard is expected to have a material impact on the Company’s financial position as virtually all leases will be recorded on the balance sheets as a right-of-use asset and a lease liability. We do not expect it to have a material impact on our results of operations or liquidity. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments. The new standard amends the current financial instrument impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables. The new standard will be effective for the Company on January 1, 2020. The adoption of this standard is not expected to have a material impact on the Company’s financial position or results of operations. In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other: Simplifying the Test for Goodwill Impairment. The new standard simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test and requires that instead, an entity should perform its goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. The new standard will be effective for the Company on January 1, 2020. The adoption of this standard is not expected to have a material impact on the Company’s financial position or results of operations. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement. The new standard modifies the disclosure requirements on fair value measurements in Topic 820, Fair Value Measurement. The standard includes changes to fair value transfers and Level 3 fair value disclosures. The new standard will be effective for the Company on January 1, 2020. The adoption of this standard is not expected to have a material impact on the Company’s financial position or results of operations. In August 2018, the FASB issued ASU No. 2018-15, Intangibles-Goodwill and Other-Internal-Use Software: Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract. The new standard aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The new standard will be effective for the Company on January 1, 2020. The Company is currently evaluating the potential impact that this standard may have on its financial position and results of operations.

Interim Consolidated Financial Statements (Policies)

9 Months Ended

Sep. 30, 2018

Accounting Policies [Abstract]

Basis of Presentation

Out of Period Adjustment

Fair Value Measurements

Adoption of New Accounting Pronouncements

The following tables summarize the effect of adopting ASC 606 on the Company’s financial statements during and as of the three and nine months ended September 30, 2018 (in thousands):

Consolidated Balance Sheet
	As of September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Accounts receivable, net	$	38,552	$	41,837
Deferred commissions		10,884		10,284
Prepaid expenses and other current assets		13,292		17,966
Total current assets		207,180		214,539
Other assets		8,417		7,855
Total assets		328,494		335,291

Deferred revenue	$	128,435	$	138,060
Total current liabilities		170,311		179,936
Total liabilities		181,664		191,289
Retained earnings		126,006		123,178
Total stockholders’ equity		146,830		144,002
Total liabilities and stockholders’ equity		328,494		335,291

Total assets were $6.8 million less than if the previous guidance remained in effect, largely due to the following changes required by the adoption of ASC 606:

•

Accounts receivable, net was lower due to the Company excluding invoices issued on cancellable contracts in excess of revenue recognized.

•

Deferred commissions was higher due to the capitalization of fringe benefits costs.

•

Prepaid expenses and other current assets were lower due to expensing survey costs as incurred and the current period tax effect of the adjustments.

Consolidated Statement of Income
	Three Months Ended September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Revenues:
Research services	$	56,332	$	55,719
Advisory services and events		28,558		28,287
Total revenues		84,890		84,006
Operating expenses:
Cost of services and fulfillment		34,361		34,838
Selling and marketing		31,051		30,871
Total operating expenses		79,948		80,245
Income from operations		4,942		3,761
Income before income taxes		5,244		4,063
Income tax provision		1,294		927
Net income		3,950		3,136
Basic income per common share	$	0.22	$	0.17
Diluted income per common share	$	0.21	$	0.17

Consolidated Statement of Income
	Nine Months Ended September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Revenues:
Research services	$	166,332	$	167,429
Advisory services and events		92,660		93,051
Total revenues		258,992		260,480
Operating expenses:
Cost of services and fulfillment		107,537		107,841
Selling and marketing		96,771		96,502
Total operating expenses		245,311		245,346
Income from operations		13,681		15,134
Income before income taxes		14,091		15,544
Income tax provision		4,086		4,564
Net income		10,005		10,980
Basic income per common share	$	0.55	$	0.61
Diluted income per common share	$	0.55	$	0.60

Consolidated Statement of Comprehensive Income
	Three Months Ended September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Net income	$	3,950	$	3,136
Comprehensive income		3,413		2,599

Consolidated Statement of Comprehensive Income
	Nine Months Ended September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Net income	$	10,005	$	10,980
Comprehensive income		7,724		8,698

Consolidated Statement of Cash Flows
	Nine Months Ended September 30, 2018
				Amounts as
				if Previous
				Guidance in
	As Reported			Effect
Cash flows from operating activities:
Net income	$	10,005		$	10,980
Accounts receivable		31,857			28,572
Deferred commissions		3,716			3,447
Prepaid expenses and other current assets		(68	)		714
Deferred revenue		(8,205	)		(6,408	)

The impact to comprehensive income and cash flows from operating activities are driven by the consolidated balance sheet and income statement changes previously discussed.

Interim Consolidated Financial Statements (Tables)

9 Months Ended

Sep. 30, 2018

ASC 606 [Member]

Summary Of Significant Accounting Policy [Line Items]

Summary of Effect of Adopting ASC 606 on Company's Financial Statements

The following tables summarize the effect of adopting ASC 606 on the Company’s financial statements during and as of the three and nine months ended September 30, 2018 (in thousands):

Consolidated Balance Sheet
	As of September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Accounts receivable, net	$	38,552	$	41,837
Deferred commissions		10,884		10,284
Prepaid expenses and other current assets		13,292		17,966
Total current assets		207,180		214,539
Other assets		8,417		7,855
Total assets		328,494		335,291

Deferred revenue	$	128,435	$	138,060
Total current liabilities		170,311		179,936
Total liabilities		181,664		191,289
Retained earnings		126,006		123,178
Total stockholders’ equity		146,830		144,002
Total liabilities and stockholders’ equity		328,494		335,291

Consolidated Statement of Income
	Three Months Ended September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Revenues:
Research services	$	56,332	$	55,719
Advisory services and events		28,558		28,287
Total revenues		84,890		84,006
Operating expenses:
Cost of services and fulfillment		34,361		34,838
Selling and marketing		31,051		30,871
Total operating expenses		79,948		80,245
Income from operations		4,942		3,761
Income before income taxes		5,244		4,063
Income tax provision		1,294		927
Net income		3,950		3,136
Basic income per common share	$	0.22	$	0.17
Diluted income per common share	$	0.21	$	0.17

Consolidated Statement of Income
	Nine Months Ended September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Revenues:
Research services	$	166,332	$	167,429
Advisory services and events		92,660		93,051
Total revenues		258,992		260,480
Operating expenses:
Cost of services and fulfillment		107,537		107,841
Selling and marketing		96,771		96,502
Total operating expenses		245,311		245,346
Income from operations		13,681		15,134
Income before income taxes		14,091		15,544
Income tax provision		4,086		4,564
Net income		10,005		10,980
Basic income per common share	$	0.55	$	0.61
Diluted income per common share	$	0.55	$	0.60

Consolidated Statement of Comprehensive Income
	Three Months Ended September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Net income	$	3,950	$	3,136
Comprehensive income		3,413		2,599

Consolidated Statement of Comprehensive Income
	Nine Months Ended September 30, 2018
			Amounts as
			if Previous
			Guidance in
	As Reported		Effect
Net income	$	10,005	$	10,980
Comprehensive income		7,724		8,698

Consolidated Statement of Cash Flows
	Nine Months Ended September 30, 2018
				Amounts as
				if Previous
				Guidance in
	As Reported			Effect
Cash flows from operating activities:
Net income	$	10,005		$	10,980
Accounts receivable		31,857			28,572
Deferred commissions		3,716			3,447
Prepaid expenses and other current assets		(68	)		714
Deferred revenue		(8,205	)		(6,408	)

Acquisitions (Tables)

9 Months Ended

Sep. 30, 2018

Business Combinations [Abstract]

Summary of Fair Value of Aggregate Consideration Paid or Payable

The following table summarizes the fair value of the aggregate consideration paid or payable for FeedbackNow (in thousands):


Cash paid at close (1)	$	8,425
Working capital adjustment (2)		798
Indemnity holdback (3)		1,485
Contingent purchase price (4)		3,015
Total	$	13,723

(1)

(2)

(3)

Approximately $0.5 million and $1.0 million of the holdback is expected to be paid during 2019 and 2020, respectively.

(4)

Summary of Preliminary Allocation of Purchase Price to Fair Value of Assets Acquired and Liabilities Assumed

The following table summarizes the preliminary allocation of the purchase price to the fair value of the assets acquired and liabilities assumed for the acquisition of FeedbackNow (in thousands):


Assets:
Cash	$	463
Accounts receivable		846
Prepaids and other current assets		465
Goodwill (1)		9,087
Acquired intangible assets (2)		4,780
Other assets		75
Total assets		15,716
Liabilities:
Accounts payable and accrued liabilities		908
Contract liabilities		260
Deferred tax liability		825
Total liabilities		1,993
Net assets acquired	$	13,723

(1) Goodwill represents the expected synergies from combining FeedbackNow with Forrester as well as the value of the acquired workforce.

Accumulated Other Comprehensive Loss (Tables)

9 Months Ended

Sep. 30, 2018

Equity [Abstract]

Schedule of Components of Accumulated Other Comprehensive Loss

The components of accumulated other comprehensive loss are as follows (in thousands):

							Total
	Net Unrealized			Cumulative			Accumulated
	Loss on Marketable			Translation			Other Comprehensive
	Investments			Adjustment			Loss
Balance at January 1, 2018	$	(115	)	$	(1,897	)	$	(2,012	)
Reclassification of stranded tax effects from tax reform		(26	)		—			(26	)
Foreign currency translation		—			(2,293	)		(2,293	)
Unrealized gain on investments, net of tax of $4		12			—			12
Balance at September 30, 2018	$	(129	)	$	(4,190	)	$	(4,319	)

							Total
	Net Unrealized			Cumulative			Accumulated
	Loss on Marketable			Translation			Other Comprehensive
	Investments			Adjustment			Loss
Balance at January 1, 2017	$	(83	)	$	(7,490	)	$	(7,573	)
Foreign currency translation		—			4,905			4,905
Unrealized gain on investments, net of tax of $29		47			—			47
Balance at September 30, 2017	$	(36	)	$	(2,585	)	$	(2,621	)

							Total
	Net Unrealized			Cumulative			Accumulated
	Loss on Marketable			Translation			Other Comprehensive
	Investments			Adjustment			Loss
Balance at July 1, 2018	$	(194	)	$	(3,588	)	$	(3,782	)
Foreign currency translation		—			(602	)		(602	)
Unrealized gain on investments, net of tax of $21		65			—			65
Balance at September 30, 2018	$	(129	)	$	(4,190	)	$	(4,319	)

							Total
	Net Unrealized			Cumulative			Accumulated
	Loss on Marketable			Translation			Other Comprehensive
	Investments			Adjustment			Loss
Balance at July 1, 2017	$	(59	)	$	(4,186	)	$	(4,245	)
Foreign currency translation		—			1,601			1,601
Unrealized gain on investments, net of tax of $14		23			—			23
Balance at September 30, 2017	$	(36	)	$	(2,585	)	$	(2,621	)

Marketable Investments (Tables)

9 Months Ended

Sep. 30, 2018

Investments Debt And Equity Securities [Abstract]

Summary of Company's Marketable Investments

The following table summarizes the Company’s marketable investments (in thousands):

	As of September 30, 2018
			Gross		Gross
	Amortized		Unrealized		Unrealized			Market
	Cost		Gains		Losses			Value
Corporate obligations	$	52,567	$	1	$	(173	)	$	52,395

	As of December 31, 2017
			Gross		Gross
	Amortized		Unrealized		Unrealized			Market
	Cost		Gains		Losses			Value
Federal agency obligations	$	1,800	$	—	$	(7	)	$	1,793
Corporate obligations		52,721		—		(181	)		52,540
Total	$	54,521	$	—	$	(188	)	$	54,333

Summary of Maturity Periods of Marketable Investments

The following table summarizes the maturity periods of the marketable investments in the Company’s portfolio as of September 30, 2018 (in thousands).

		FY 2018				FY 2019				FY2020				Total
Corporate obligations		$	19,786			$	26,833			$	5,776			$	52,395

Summary of Gross Unrealized Losses and Market Value of Available-for-Sale Securities with Unrealized Losses

	As of September 30, 2018
	Less Than 12 Months				12 Months or Greater
	Market		Unrealized		Market		Unrealized
	Value		Losses		Value		Losses
Corporate obligations	$	26,181	$	32	$	24,202	$	141

	As of December 31, 2017
	Less Than 12 Months				12 Months or Greater
	Market		Unrealized		Market		Unrealized
	Value		Losses		Value		Losses
Federal agency obligations	$	—	$	—	$	1,793	$	7
Corporate obligations		31,723		149		20,817		32
Total	$	31,723	$	149	$	22,610	$	39

Summary of Company's Fair Value Hierarchy for its Financial Assets

The following table represents the Company’s fair value hierarchy for its financial assets (cash equivalents and investments) measured at fair value on a recurring basis (in thousands):

	As of September 30, 2018
	Level 1		Level 2		Level 3		Total
Money market funds (1)	$	2,952	$	—	$	—	$	2,952
Corporate obligations		—		52,395		—		52,395
Total	$	2,952	$	52,395	$	—	$	55,347

	As of December 31, 2017
	Level 1		Level 2		Level 3		Total
Money market funds (1)	$	492	$	—	$	—	$	492
Federal agency obligations		—		1,793		—		1,793
Corporate obligations		—		52,540		—		52,540
Total	$	492	$	54,333	$	—	$	54,825

(1)	Included in cash and cash equivalents.

Net Income Per Common Share (Tables)

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Schedule of Basic and Diluted Weighted Average Common Shares

Basic and diluted weighted average common shares are as follows (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Basic weighted average common shares outstanding		18,088		17,747		18,030		17,897
Weighted average common equivalent shares		345		304		323		315
Diluted weighted average common shares outstanding		18,433		18,051		18,353		18,212
Options excluded from diluted weighted average share calculation as effect would have been anti-dilutive		1		27		10		177

Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2018

Equity [Abstract]

Schedule of Restricted Stock Unit Activity

Restricted stock unit activity for the nine months ended September 30, 2018 is presented below (in thousands, except per share data):

				Weighted-
				Average
	Number of			Grant Date
	Shares			Fair Value
Unvested at December 31, 2017		509		$	37.59
Granted		245			44.01
Vested		(193	)		36.99
Forfeited		(35	)		37.20
Unvested at September 30, 2018		526		$	40.83

Schedule of Stock Option Activity

Stock option activity for the nine months ended September 30, 2018 is presented below (in thousands, except per share data and contractual term):

				Weighted -		Weighted -
				Average		Average
				Exercise		Remaining		Aggregate
	Number			Price Per		Contractual		Intrinsic
	of Shares			Share		Term (in years)		Value
Outstanding at December 31, 2017		937		$	35.10
Granted		—			—
Exercised		(267	)		34.92
Forfeited		(24	)		35.39
Outstanding at September 30, 2018		646		$	35.17		5.27	$	6,936
Exercisable at September 30, 2018		538		$	35.31		4.92	$	5,702
Vested and expected to vest at September 30, 2018		646		$	35.17		5.27	$	6,936

Summary of Stock-Based Compensation Recorded in Expense Categories

Stock-based compensation was recorded in the following expense categories (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Cost of services and fulfillment	$	1,001	$	1,088	$	3,128	$	3,387
Selling and marketing		261		170		752		535
General and administrative		858		920		2,311		2,501
Total	$	2,120	$	2,178	$	6,191	$	6,423

Shares Subject to Employee Stock Purchase Plan Valuation Assumptions

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2018			2017			2018			2017
Average risk-free interest rate		2.34	%		0.96	%		1.80	%		0.81	%
Expected dividend yield		1.6	%		1.9	%		1.9	%		1.9	%
Expected life	0.5 Years			0.5 Years			0.5 Years			0.5 Years
Expected volatility		25	%		26	%		22	%		24	%
Weighted average fair value	$	10.87		$	8.50		$	8.72		$	8.32

Operating Segments (Tables)

9 Months Ended

Sep. 30, 2018

Segment Reporting [Abstract]

Schedule of Information about Reportable Segments

The Company is providing disaggregated revenue by product in the segment tables below in accordance with the revenue standard adopted on January 1, 2018.

						Project
	Product		Research			Consulting		Consolidated
Three Months Ended September 30, 2018
Research services revenues
Research	$	38,309	$	—		$	—	$	38,309
Connect		12,780		—			—		12,780
Analytics		5,243		—			—		5,243
Total research services revenues		56,332		—			—		56,332

Advisory services and events revenues
Advisory services		—		9,171			154		9,325
Consulting services		2,030		2,517			13,771		18,318
Events		915		—			—		915
Total advisory services and events revenues		2,945		11,688			13,925		28,558
Total segment revenues		59,277		11,688			13,925		84,890
Segment expenses		11,521		12,688			7,012		31,221
Contribution margin (loss)		47,756		(1,000	)		6,913		53,669
Selling, marketing, administrative and other expenses									(47,348	)
Amortization of intangible assets									(402	)
Acquisition and integration cost									(977	)
Other income and losses on investments									302
Income before income taxes								$	5,244

						Project
	Product		Research			Consulting		Consolidated
Three Months Ended September 30, 2017
Research services revenues
Research	$	36,894	$	—		$	—	$	36,894
Connect		12,506		—			—		12,506
Analytics		4,835		—			—		4,835
Total research services revenues		54,235		—			—		54,235

Advisory services and events revenues
Advisory services		—		8,297			81		8,378
Consulting services		2,250		2,082			12,321		16,653
Events		1,103		—			—		1,103
Total advisory services and events revenues		3,353		10,379			12,402		26,134
Total segment revenues		57,588		10,379			12,402		80,369
Segment expenses		9,764		11,953			6,443		28,160
Contribution margin (loss)		47,824		(1,574	)		5,959		52,209
Selling, marketing, administrative and other expenses									(45,263	)
Amortization of intangible assets									(197	)
Acquisition and integration cost									—
Other income and losses on investments									(626	)
Income before income taxes								$	6,123

						Project
	Product		Research			Consulting		Consolidated
Nine Months Ended September 30, 2018
Research services revenues
Research	$	114,007	$	—		$	—	$	114,007
Connect		37,882		—			—		37,882
Analytics		14,443		—			—		14,443
Total research services revenues		166,332		—			—		166,332

Advisory services and events revenues
Advisory services		—		29,664			290		29,954
Consulting services		6,079		7,306			40,397		53,782
Events		8,924		—			—		8,924
Total advisory services and events revenues		15,003		36,970			40,687		92,660
Total segment revenues		181,335		36,970			40,687		258,992
Segment expenses		36,534		38,182			20,930		95,646
Contribution margin (loss)		144,801		(1,212	)		19,757		163,346
Selling, marketing, administrative and other expenses									(147,589	)
Amortization of intangible assets									(770	)
Acquisition and integration cost									(1,306	)
Other income and losses on investments									410
Income before income taxes								$	14,091

						Project
	Products		Research			Consulting		Consolidated
Nine Months Ended September 30, 2017
Research services revenues
Research	$	110,550	$	—		$	—	$	110,550
Connect		36,103		—			—		36,103
Analytics		13,900		—			—		13,900
Total research services revenues		160,553		—			—		160,553

Advisory services and events revenues
Advisory services		—		25,889			254		26,143
Consulting services		7,495		6,390			38,496		52,381
Events		8,219		—			—		8,219
Total advisory services and events revenues		15,714		32,279			38,750		86,743
Total segment revenues		176,267		32,279			38,750		247,296
Segment expenses		32,788		36,510			18,886		88,184
Contribution margin (loss)		143,479		(4,231	)		19,864		159,112
Selling, marketing, administrative and other expenses									(138,432	)
Amortization of intangible assets									(582	)
Acquisition and integration cost									—
Other income and losses on investments									(749	)
Income before income taxes								$	19,349

Interim Consolidated Financial Statements - Additional Information (Detail) - USD ($)		3 Months Ended				9 Months Ended		12 Months Ended
	Jan. 02, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Summary Of Significant Accounting Policy [Line Items]
Deferred revenue		$ 128,435,000				$ 128,435,000		$ 145,207,000
Prepaid expenses and other current assets		13,292,000				13,292,000		18,942,000
Deferred commissions		10,884,000				10,884,000		13,731,000
Other assets		8,417,000				8,417,000		6,231,000
Retained earnings		126,006,000				126,006,000		123,010,000
Total assets		328,494,000				328,494,000		345,200,000
Total revenues		84,890,000			$ 80,369,000	258,992,000	$ 247,296,000
Net income		$ 3,950,000			$ 3,953,000	$ 10,005,000	$ 13,047,000
Diluted net income per share		$ 0.21			$ 0.22	$ 0.55	$ 0.72
ASU No. 2018-02 [Member]
Summary Of Significant Accounting Policy [Line Items]
Reclassification adjustment to retained earnings for tax effects	$ 26,000
ASC 606 [Member] \| Initial Application Period Cumulative Effect Transition [Member]
Summary Of Significant Accounting Policy [Line Items]
Deferred revenue		$ 7,800,000				$ 7,800,000
Prepaid expenses and other current assets		(5,500,000)				(5,500,000)
Deferred commissions		900,000				900,000
Other assets		600,000				600,000
Retained earnings		3,800,000				3,800,000
ASC 606 [Member] \| Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Summary Of Significant Accounting Policy [Line Items]
Deferred revenue		(9,600,000)				(9,600,000)
Total assets		(6,800,000)				(6,800,000)
Total revenues		(900,000)				(1,500,000)
Net income		$ (800,000)				$ (1,000,000)
Diluted net income per share		$ 0.04				$ 0.05
Research Services [Member]
Summary Of Significant Accounting Policy [Line Items]
Out-of-period correction revenue			$ 1,000,000
Out-of-period correction revenue, after tax			$ 700,000
Total revenues		$ 56,332,000			$ 54,235,000	$ 166,332,000	$ 160,553,000
Understatement of Revenue from Reprint Product Line [Member]
Summary Of Significant Accounting Policy [Line Items]
Out-of-period correction revenue				$ 800,000				200,000
Out-of-period correction revenue, after tax				$ 500,000				$ 100,000

Interim Consolidated Financial Statements - Summary of Effect of Adopting ASC 606 In Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts receivable, net	$ 38,552	$ 70,023
Deferred commissions	10,884	13,731
Prepaid expenses and other current assets	13,292	18,942
Total current assets	207,180	236,819
Other assets	8,417	6,231
Total assets	328,494	345,200
Deferred revenue	128,435	145,207
Total current liabilities	170,311	195,053
Total liabilities	181,664	204,011
Retained earnings	126,006	123,010
Total stockholders’ equity	146,830	141,189
Total liabilities and stockholders’ equity	328,494	$ 345,200
ASC 606 [Member] \| Amounts as if Previous Guidance in Effect [Member]
Accounts receivable, net	41,837
Deferred commissions	10,284
Prepaid expenses and other current assets	17,966
Total current assets	214,539
Other assets	7,855
Total assets	335,291
Deferred revenue	138,060
Total current liabilities	179,936
Total liabilities	191,289
Retained earnings	123,178
Total stockholders’ equity	144,002
Total liabilities and stockholders’ equity	$ 335,291

Interim Consolidated Financial Statements - Summary of Effect of Adopting ASC 606 In Consolidated Statement of Income (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Total revenues	$ 84,890	$ 80,369	$ 258,992	$ 247,296
Operating expenses:
Selling and marketing	31,051	29,225	96,771	90,355
Total operating expenses	79,948	73,620	245,311	227,198
Income from operations	4,942	6,749	13,681	20,098
Income before income taxes	5,244	6,123	14,091	19,349
Income tax provision	1,294	2,170	4,086	6,302
Net income	$ 3,950	$ 3,953	$ 10,005	$ 13,047
Basic income per common share	$ 0.22	$ 0.22	$ 0.55	$ 0.73
Diluted income per common share	$ 0.21	$ 0.22	$ 0.55	$ 0.72
Research Services [Member]
Revenues:
Total revenues	$ 56,332	$ 54,235	$ 166,332	$ 160,553
Advisory Services and Events [Member]
Revenues:
Total revenues	28,558	26,134	92,660	86,743
Cost of Services and Fulfillment [Member]
Operating expenses:
Cost of services and fulfillment	34,361	$ 32,508	107,537	$ 100,814
ASC 606 [Member] \| Amounts as if Previous Guidance in Effect [Member]
Revenues:
Total revenues	84,006		260,480
Operating expenses:
Selling and marketing	30,871		96,502
Total operating expenses	80,245		245,346
Income from operations	3,761		15,134
Income before income taxes	4,063		15,544
Income tax provision	927		4,564
Net income	$ 3,136		$ 10,980
Basic income per common share	$ 0.17		$ 0.61
Diluted income per common share	$ 0.17		$ 0.60
ASC 606 [Member] \| Research Services [Member] \| Amounts as if Previous Guidance in Effect [Member]
Revenues:
Total revenues	$ 55,719		$ 167,429
ASC 606 [Member] \| Advisory Services and Events [Member] \| Amounts as if Previous Guidance in Effect [Member]
Revenues:
Total revenues	28,287		93,051
ASC 606 [Member] \| Cost of Services and Fulfillment [Member] \| Amounts as if Previous Guidance in Effect [Member]
Operating expenses:
Cost of services and fulfillment	$ 34,838		$ 107,841

Interim Consolidated Financial Statements - Summary of Effect of Adopting ASC 606 In Consolidated Statement of Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net income	$ 3,950	$ 3,953	$ 10,005	$ 13,047
Comprehensive income	3,413	$ 5,577	7,724	$ 17,999
ASC 606 [Member] \| Amounts as if Previous Guidance in Effect [Member]
Net income	3,136		10,980
Comprehensive income	$ 2,599		$ 8,698

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Interim Consolidated Financial Statements - Summary of Effect of Adopting ASC 606 In Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 3,950	$ 3,953	$ 10,005	$ 13,047
Accounts receivable			31,857	20,140
Deferred commissions			3,716	2,906
Prepaid expenses and other current assets			(68)	(979)
Deferred revenue			(8,205)	$ (3,473)
ASC 606 [Member] \| Amounts as if Previous Guidance in Effect [Member]
Cash flows from operating activities:
Net income	$ 3,136		10,980
Accounts receivable			28,572
Deferred commissions			3,447
Prepaid expenses and other current assets			714
Deferred revenue			$ (6,408)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Acquisitions - Additional Information (Detail) - USD ($)			3 Months Ended	9 Months Ended
	Jul. 06, 2018	Jun. 22, 2018	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill			$ 85,126,000	$ 85,126,000	$ 76,169,000
Increase (decrease) in goodwill				9,000,000
Decrease in goodwill due to foreign currency fluctuations				$ 800,000
SocialGlimpz Inc. [Member]
Business Acquisition [Line Items]
Acquisition date		Jun. 22, 2018
Name of the business entity acquired				SocialGlimpz Inc.
Description of acquired entity				On June 22, 2018, Forrester acquired substantially all of the assets of SocialGlimpz Inc. (“GlimpzIt”), an artificial intelligence and machine-learning provider based in San Francisco. The acquisition is part of Forrester's plan to build a real-time customer experience or CX cloud solution, integrating a range of inputs to help companies monitor and improve customer experience. Forrester intends to deploy the GlimpzIt technology to extend the analytics engine in Forrester’s planned real-time CX cloud.
Purchase price paid		$ 1,300,000
Goodwill		700,000
Cash contingent to be paid on achievement of certain employment conditions		$ 300,000
Compensation expense to be recognized over related service period of employees		2 years
SocialGlimpz Inc. [Member] \| Technology [Member]
Business Acquisition [Line Items]
Intangible assets		$ 600,000
Estimated useful life		5 years
FeedbackNow [Member]
Business Acquisition [Line Items]
Acquisition date	Jul. 06, 2018
Purchase price paid	$ 8,425,000
Goodwill	$ 9,087,000
Percentage of shares acquired	100.00%
Acquisition price due and subject to indemnity provisions from seller	$ 1,485,000
Additional purchase price payable based on acquired working capital	$ 798,000
Balance acquisition price payable period	2 years
Maximum consideration payable based on the financial performance of acquired company	$ 4,200,000
Revenue			500,000
Direct expenses			1,100,000
Acquisition costs recognized			$ 100,000	$ 400,000
SocialGlimpz Inc and FeedbackNow [Member]
Business Acquisition [Line Items]
Increase (decrease) in goodwill				$ 9,800,000

Acquisitions - Summary of Fair Value of Aggregate Consideration Paid or Payable (Detail) - FeedbackNow [Member] $ in Thousands	Jul. 06, 2018 USD ($)
Business Acquisition [Line Items]
Cash paid at close	$ 8,425
Working capital adjustment	798
Indemnity holdback	1,485
Contingent purchase price	3,015
Total	$ 13,723

Acquisitions - Summary of Fair Value of Aggregate Consideration Paid or Payable (Parenthetical) (Detail) - USD ($)		9 Months Ended	12 Months Ended
	Jul. 06, 2018	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Net cash paid		$ 9,250,000
FeedbackNow [Member]
Business Acquisition [Line Items]
Cash acquired	$ 500,000
Net cash paid	8,000,000
Holdback amount expected to be paid	1,485,000
Business acquisition undiscounted amounts could be payable, minimum	0
Business acquisition undiscounted amounts could be payable, maximum	4,200,000
Contingent purchase price	$ 3,015,000
FeedbackNow [Member] \| Scenario Forecast [Member]
Business Acquisition [Line Items]
Holdback amount expected to be paid			$ 1,000,000	$ 500,000
FeedbackNow [Member] \| Maximum [Member] \| Scenario Forecast [Member]
Business Acquisition [Line Items]
Additional consideration payable to sellers based on financial performance			$ 2,500,000	$ 1,700,000

Acquisitions - Summary of Preliminary Allocation of Purchase Price to Fair Value of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jul. 06, 2018	Dec. 31, 2017
Assets:
Goodwill	$ 85,126		$ 76,169
FeedbackNow [Member]
Assets:
Cash		$ 463
Accounts receivable		846
Prepaids and other current assets		465
Goodwill		9,087
Acquired intangible assets		4,780
Other assets		75
Total assets		15,716
Liabilities:
Accounts payable and accrued liabilities		908
Contract liabilities		260
Deferred tax liability		825
Total liabilities		1,993
Net assets acquired		$ 13,723

Acquisitions - Summary of Preliminary Allocation of Purchase Price to Fair Value of Assets Acquired and Liabilities Assumed (Parenthetical) (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Jul. 06, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Amortization of intangible assets		$ 402	$ 197	$ 770	$ 582
FeedbackNow [Member]
Business Acquisition [Line Items]
Acquired intangible assets	$ 4,780
Amortization of intangible assets		$ 200		$ 200
FeedbackNow [Member] \| Technology Asset Class [Member]
Business Acquisition [Line Items]
Acquired intangible assets	$ 3,000
Acquired intangible assets, Useful life	6 years 6 months
FeedbackNow [Member] \| Customer Relationships [Member]
Business Acquisition [Line Items]
Acquired intangible assets	$ 1,300
Acquired intangible assets, Useful life	4 years 6 months
FeedbackNow [Member] \| Trade Names [Member]
Business Acquisition [Line Items]
Acquired intangible assets	$ 500
Acquired intangible assets, Useful life	8 years 6 months

Accumulated Other Comprehensive Loss - Schedule of Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ (2,012)
Reclassification of stranded tax effects from tax reform			(26)
Foreign currency translation	$ (602)	$ 1,601	(2,293)	$ 4,905
Unrealized gain on investments, net of tax	65	23	12	47
Ending Balance	(4,319)		(4,319)
Beginning Balance			141,189
Ending Balance	146,830		146,830
Net Unrealized Loss on Marketable Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(194)	(59)	(115)	(83)
Reclassification of stranded tax effects from tax reform			(26)
Unrealized gain on investments, net of tax	65	23	12	47
Ending Balance	(129)	(36)	(129)	(36)
Cumulative Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(3,588)	(4,186)	(1,897)	(7,490)
Foreign currency translation	(602)	1,601	(2,293)	4,905
Ending Balance	(4,190)	(2,585)	(4,190)	(2,585)
Total Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(3,782)	(4,245)	(2,012)	(7,573)
Ending Balance	$ (4,319)	$ (2,621)	$ (4,319)	$ (2,621)

Accumulated Other Comprehensive Loss - Schedule of Components of Accumulated Other Comprehensive Loss (Detail) (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Comprehensive Income Loss Tax Parenthetical Disclosures [Abstract]
Tax expense (benefit) on unrealized gain (loss) on investments	$ 21	$ 14	$ 4	$ 29

Marketable Investments - Summary of Company's Marketable Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 54,521
Gross Unrealized Losses		(188)
Market Value	$ 52,395	54,333
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	52,567	52,721
Gross Unrealized Gains	1
Gross Unrealized Losses	(173)	(181)
Market Value	$ 52,395	52,540
Federal Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,800
Gross Unrealized Losses		(7)
Market Value		$ 1,793

Marketable Investments - Summary of Maturity Periods of the Marketable Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Total	$ 52,395	$ 54,333
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
FY 2018	19,786
FY 2019	26,833
FY2020	5,776
Total	$ 52,395	$ 52,540

Marketable Investments - Summary of Gross Unrealized Losses and Market Value of Available-for-Sale Securities with Unrealized Losses (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less Than 12 Months, Market Value		$ 31,723
Available for sale securities, Less Than 12 Months, Unrealized Losses		149
Available for sale securities, 12 Months or Greater, Market Value		22,610
Available for sale securities, 12 Months or Greater, Unrealized Losses		39
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, Less Than 12 Months, Market Value	$ 26,181	31,723
Available for sale securities, Less Than 12 Months, Unrealized Losses	32	149
Available for sale securities, 12 Months or Greater, Market Value	24,202	20,817
Available for sale securities, 12 Months or Greater, Unrealized Losses	$ 141	32
Federal Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, 12 Months or Greater, Market Value		1,793
Available for sale securities, 12 Months or Greater, Unrealized Losses		$ 7

Marketable Investments - Summary of Company's Fair Value Hierarchy for its Financial Assets (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets	$ 55,347	$ 54,825
Corporate Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of investments	52,395	52,540
Federal Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of investments		1,793
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets	2,952	492
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of investments	52,395	54,333
Level 2 [Member] \| Corporate Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of investments	52,395	52,540
Level 2 [Member] \| Federal Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of investments		1,793
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of cash equivalents	2,952	492
Money Market Funds [Member] \| Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of cash equivalents	$ 2,952	$ 492

Non-Marketable Investments - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]
Carrying value of the Company's non-marketable investments	$ 1,800,000		$ 1,800,000		$ 1,900,000
Losses from non-marketable investments		$ (800,000)	(100,000)	$ (1,000,000)
Distributions received from funds	$ 0	$ 0	$ 0	$ 400,000
Limited Partnerships Investments [Member] \| Minimum [Member]
Fair Value Investments Entities That Calculate Net Asset Value Per Share [Line Items]
Ownership interest of Company			5.00%

Revenue and Contract Costs - Additional Information (Detail)	3 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract assets	$ 0	$ 0
Contract with customer, contract duration		1 year
Deferred revenue recognized	24,700,000	$ 128,600,000
Revenue expected to be recognized	251,200,000	251,200,000
Amortization expense related to deferred commissions	$ 7,200,000	$ 22,400,000
Minimum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Advisory services period		1 hour
Consulting services period		14 days
Performance obligation, revenue expected to be recognized	12 months	12 months
Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Advisory services period		2 days
Consulting services period		3 months
Contract with customer, expected payment term		one year
Performance obligation, revenue expected to be recognized	24 months	24 months

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Income tax expense	$ 1,294	$ 2,170	$ 4,086	$ 6,302
Effective income tax rate			29.00%	32.60%
Income tax expense decreased due to decrease in federal tax rate due to Tax Cuts and Jobs Act			$ 2,200
Settlement from Tax Audit [Member]
Income Taxes [Line Items]
Tax benefit recognized						$ 1,300
Anticipated [Member]
Income Taxes [Line Items]
Effective income tax rate					31.00%

Net Income Per Common Share - Schedule of Basic and Diluted Weighted Average Common Shares (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Basic weighted average common shares outstanding	18,088	17,747	18,030	17,897
Weighted average common equivalent shares	345	304	323	315
Diluted weighted average common shares outstanding	18,433	18,051	18,353	18,212
Options excluded from diluted weighted average share calculation as effect would have been anti-dilutive	1	27	10	177

Stockholders' Equity - Schedule of Restricted Stock Unit Activity (Detail) - Restricted Stock Units (RSUs) [Member] shares in Thousands	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested at December 31, 2017 \| shares	509
Number of Shares, Granted \| shares	245
Number of Shares, Vested \| shares	(193)
Number of Shares, Forfeited \| shares	(35)
Number of Shares, Unvested at September 30, 2018 \| shares	526
Weighted-Average Grant Date Fair Value, Unvested, Beginning Balance \| $ / shares	$ 37.59
Weighted-Average Grant Date Fair Value, Granted \| $ / shares	44.01
Weighted-Average Grant Date Fair Value, Vested \| $ / shares	36.99
Weighted-Average Grant Date Fair Value, Forfeited \| $ / shares	37.20
Weighted-Average Grant Date Fair Value, Unvested, Ending Balance \| $ / shares	$ 40.83

Stockholders' Equity - Schedule of Stock Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Outstanding at December 31, 2017 \| shares	937
Number of Shares, Exercised \| shares	(267)
Number of Shares, Forfeited \| shares	(24)
Number of Shares, Outstanding at September 30, 2018 \| shares	646
Number of Shares, Exercisable at September 30, 2018 \| shares	538
Number of Shares, Vested and expected to vest at September 30, 2018 \| shares	646
Weighted - Average Exercise Price Per Share, Outstanding, Beginning balance \| $ / shares	$ 35.10
Weighted - Average Exercise Price Per Share, Exercised \| $ / shares	34.92
Weighted - Average Exercise Price Per Share, Forfeited \| $ / shares	35.39
Weighted - Average Exercise Price Per Share, Outstanding, Ending balance \| $ / shares	35.17
Weighted - Average Exercise Price Per Share, Exercisable at September 30, 2018 \| $ / shares	35.31
Weighted - Average Exercise Price Per Share, Vested and expected to vest at September 30, 2018 \| $ / shares	$ 35.17
Weighted - Average Remaining Contractual Term, Outstanding at September 30, 2018	5 years 3 months 7 days
Weighted - Average Remaining Contractual Term, Exercisable at September 30, 2018	4 years 11 months 1 day
Weighted - Average Remaining Contractual Term, Vested and expected to vest at September 30, 2018	5 years 3 months 7 days
Aggregate Intrinsic Value, Outstanding at September 30, 2018 \| $	$ 6,936
Aggregate Intrinsic Value, Exercisable at September 30, 2018 \| $	5,702
Aggregate Intrinsic Value, Vested and expected to vest at September 30, 2018 \| $	$ 6,936

Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended						9 Months Ended
	Oct. 31, 2018	May 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Feb. 28, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, par value			$ 0.01						$ 0.01			$ 0.01
Dividend declared and paid per share			0.20	$ 0.20	$ 0.20	$ 0.19	$ 0.19	$ 0.19
Aggregate dividend declared for the year									$ 10,800,000	$ 10,200,000
Dividend declared per share			$ 0.20			$ 0.19			$ 0.60	$ 0.57
Authorized to purchase of common stock under the stock repurchase program			$ 535,000,000						$ 535,000,000		$ 50,000,000
Repurchase of common Stock						100,000			200,000	1,100,000
Cumulative aggregate cost of repurchase of common stock			$ 300,000			$ 3,500,000			$ 10,000,000	$ 40,000,000
Cumulative repurchase of common stock			16,300,000						16,300,000
Aggregate cost of repurchase of common stock									$ 474,900,000
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend declared per share	$ 0.20
Dividend payable, date declared	2018-10
Dividend declared payable date	Dec. 26, 2018
Dividend payable, record date	Dec. 12, 2018
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares to be granted		400,000
Common stock, par value		$ 0.01

Stockholders' Equity - Summary of Stock-Based Compensation Recorded in Expense Categories (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total allocated share-based compensation expense	$ 2,120	$ 2,178	$ 6,191	$ 6,423
Cost of Services and Fulfillment [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total allocated share-based compensation expense	1,001	1,088	3,128	3,387
Selling and Marketing [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total allocated share-based compensation expense	261	170	752	535
General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total allocated share-based compensation expense	$ 858	$ 920	$ 2,311	$ 2,501

Stockholders' Equity - Shares Subject to Employee Stock Purchase Plan Valuation Assumptions (Detail) - Employee Stock Purchase Plan [Member] - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Average risk-free interest rate	2.34%	0.96%	1.80%	0.81%
Expected dividend yield	1.60%	1.90%	1.90%	1.90%
Expected life	6 months	6 months	6 months	6 months
Expected volatility	25.00%	26.00%	22.00%	24.00%
Weighted average fair value	$ 10.87	$ 8.50	$ 8.72	$ 8.32

Operating Segments - Schedule of Information about Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Total revenues	$ 84,890	$ 80,369	$ 258,992	$ 247,296
Segment expenses	31,221	28,160	95,646	88,184
Contribution margin (loss)	53,669	52,209	163,346	159,112
Selling, marketing, administrative and other expenses	(47,348)	(45,263)	(147,589)	(138,432)
Amortization of intangible assets	(402)	(197)	(770)	(582)
Acquisition and integration cost	(977)		(1,306)
Other income and losses on investments	302	(626)	410	(749)
Income before income taxes	5,244	6,123	14,091	19,349
Research [Member]
Segment Reporting Information [Line Items]
Total revenues	38,309	36,894	114,007	110,550
Connect [Member]
Segment Reporting Information [Line Items]
Total revenues	12,780	12,506	37,882	36,103
Analytics [Member]
Segment Reporting Information [Line Items]
Total revenues	5,243	4,835	14,443	13,900
Research Services [Member]
Segment Reporting Information [Line Items]
Total revenues	56,332	54,235	166,332	160,553
Advisory Services [Member]
Segment Reporting Information [Line Items]
Total revenues	9,325	8,378	29,954	26,143
Consulting Services [Member]
Segment Reporting Information [Line Items]
Total revenues	18,318	16,653	53,782	52,381
Events [Member]
Segment Reporting Information [Line Items]
Total revenues	915	1,103	8,924	8,219
Advisory Services and Events [Member]
Segment Reporting Information [Line Items]
Total revenues	28,558	26,134	92,660	86,743
Product Organization [Member]
Segment Reporting Information [Line Items]
Total revenues	59,277	57,588	181,335	176,267
Segment expenses	11,521	9,764	36,534	32,788
Contribution margin (loss)	47,756	47,824	144,801	143,479
Product Organization [Member] \| Research [Member]
Segment Reporting Information [Line Items]
Total revenues	38,309	36,894	114,007	110,550
Product Organization [Member] \| Connect [Member]
Segment Reporting Information [Line Items]
Total revenues	12,780	12,506	37,882	36,103
Product Organization [Member] \| Analytics [Member]
Segment Reporting Information [Line Items]
Total revenues	5,243	4,835	14,443	13,900
Product Organization [Member] \| Research Services [Member]
Segment Reporting Information [Line Items]
Total revenues	56,332	54,235	166,332	160,553
Product Organization [Member] \| Consulting Services [Member]
Segment Reporting Information [Line Items]
Total revenues	2,030	2,250	6,079	7,495
Product Organization [Member] \| Events [Member]
Segment Reporting Information [Line Items]
Total revenues	915	1,103	8,924	8,219
Product Organization [Member] \| Advisory Services and Events [Member]
Segment Reporting Information [Line Items]
Total revenues	2,945	3,353	15,003	15,714
Research Organization [Member]
Segment Reporting Information [Line Items]
Total revenues	11,688	10,379	36,970	32,279
Segment expenses	12,688	11,953	38,182	36,510
Contribution margin (loss)	(1,000)	(1,574)	(1,212)	(4,231)
Research Organization [Member] \| Advisory Services [Member]
Segment Reporting Information [Line Items]
Total revenues	9,171	8,297	29,664	25,889
Research Organization [Member] \| Consulting Services [Member]
Segment Reporting Information [Line Items]
Total revenues	2,517	2,082	7,306	6,390
Research Organization [Member] \| Advisory Services and Events [Member]
Segment Reporting Information [Line Items]
Total revenues	11,688	10,379	36,970	32,279
Project Consulting [Member]
Segment Reporting Information [Line Items]
Total revenues	13,925	12,402	40,687	38,750
Segment expenses	7,012	6,443	20,930	18,886
Contribution margin (loss)	6,913	5,959	19,757	19,864
Project Consulting [Member] \| Advisory Services [Member]
Segment Reporting Information [Line Items]
Total revenues	154	81	290	254
Project Consulting [Member] \| Consulting Services [Member]
Segment Reporting Information [Line Items]
Total revenues	13,771	12,321	40,397	38,496
Project Consulting [Member] \| Advisory Services and Events [Member]
Segment Reporting Information [Line Items]
Total revenues	$ 13,925	$ 12,402	$ 40,687	$ 38,750