Acquisitions (Details) (USD $)	12 Months Ended				1 Months Ended			6 Months Ended	1 Months Ended	9 Months Ended
	Dec. 31, 2014 business		Dec. 31, 2013	Dec. 31, 2012 business	Jun. 30, 2014 employee	Oct. 31, 2014	May 31, 2014 employee	Dec. 31, 2014	Mar. 31, 2014 employee	Dec. 31, 2014
Business Acquisition [Line Items]
Number of businesses acquired	3			1
Cash payment to acquire business	$ 114,600,000
Acquisition and integration charges	21,867,000		337,000	2,420,000
Acquisitions - cash plaid (net of cash acquired)	109,928,000		0	10,336,000
Acquisition and integration charges	21,867,000		337,000	2,420,000
Goodwill acquired	78,373,000	[1]
Additions due to acquisition	31,975,000	[2]
Senexx, Ltd.
Business Acquisition [Line Items]
Number of employees					2
Cash payment to acquire business					4,900,000
Percentage of voting interests acquired					100.00%
Acquisitions cash place in escrow					800,000
Payments to acquired business, gross, including cash placed in escrow					5,700,000
Escrow balance payment period					18 months
Market-Visio Oy
Business Acquisition [Line Items]
Number of employees							68
Cash payment to acquire business							4,100,000
Percentage of voting interests acquired							100.00%
Business combination consideration							6,500,000
Decrease in contingent liability						2,400,000
Goodwill adjustment increase (decrease)								(100,000)
SircleIT Inc.
Business Acquisition [Line Items]
Goodwill adjustment increase (decrease)								(200,000)
Software Advice
Business Acquisition [Line Items]
Number of employees									120
Cash payment to acquire business									103,200,000
Percentage of voting interests acquired									100.00%
Consideration transferred, additional obligated amount									31,900,000
Acquisitions cash place in escrow									13,500,000
Contingent consideration amount maximum									18,400,000
Expensed liability time period									2 years
Goodwill adjustment increase (decrease)										2,700,000
Intangible assets decrease adjustment								2,700,000
Goodwill deductible period	15 years
Total
Business Acquisition [Line Items]
Cash acquired	4,700,000
Ideas International
Business Acquisition [Line Items]
Cash payment to acquire business				18,800,000
Percentage of voting interests acquired				100.00%
Acquisition and integration charges			300,000	2,400,000
Goodwill acquired				7,500,000
Additions due to acquisition				$ 8,500,000

[1] The addition is due to the 2014 Acquisitions (See Note 2—Acquisitions for additional discussion). All of the recorded goodwill from these acquisitions has been included in the Research segment.

[2] The additions are due to the Company's 2014 Acquisitions. See Note 2 — Acquisitions for additional information.