Acquisition and Disposition (Details) - USD ($) $ in Thousands			9 Months Ended	12 Months Ended
	Apr. 14, 2015	Mar. 16, 2015	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Recognized amounts of tangible assets and liabilities:
Goodwill			$ 218,972	$ 218,972	$ 398,164	$ 398,164
Sale of business
Loss on sale				9,501	$ 0	$ 0
3Q Digital Inc
Acquisition and Disposition
Deferred Taxes, Business Combination, Valuation Allowance, Available to Reduce Goodwill		$ 2,299
Estimate of potential undiscounted future contingent consideration payments, low end of range		0
Estimate of potential undiscounted future contingent consideration payments, high end of range		35,000
Total consideration
Cash consideration per purchase agreement		30,245
Estimated fair value of contingent consideration		17,940
Identifiable intangible assets and goodwill		48,185
Recognized amounts of tangible assets and liabilities:
Current assets		4,135
Property and equipment		164
Other assets		389
Current liabilities		(822)
Total tangible assets and liabilities:		3,866
Identifiable intangible assets		4,773
Goodwill		41,845
Total		50,484
3Q Digital Inc | Customer relationships
Total consideration
Identifiable intangible assets and goodwill		48,185
Recognized amounts of tangible assets and liabilities:
Identifiable intangible assets		$ 4,300
Amortization period		7 years
3Q Digital Inc | Tradenames and trademarks
Recognized amounts of tangible assets and liabilities:
Identifiable intangible assets		$ 300
Amortization period		2 years
3Q Digital Inc | Non-compete agreements
Recognized amounts of tangible assets and liabilities:
Identifiable intangible assets		$ 200
Amortization period		3 years
3Q Digital Inc | Level 3 | Contingent Consideration
Reconciliation of accrued earnout consideration
Contingent consideration at acquisition date			17,940
Accretion of interest			2,337
Contingent consideration at December 31, 2015		$ 17,940	$ 20,277	$ 20,277
Maximum
Recognized amounts of tangible assets and liabilities:
Amortization period					10 years
B2B research business
Sale of business
Loss on sale	$ 9,500
B2B research business | Maximum
Sale of business
Percent of total Company revenue (less than)					5.00%