Basis of Condensed Consolidated Financial Statements (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($) customer	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($) customer	Dec. 31, 2016 USD ($)
Accounts payable and accrued expenses	$ 144,902	$ 144,902		$ 144,902		$ 168,284
Equity in earnings/(losses) of affiliates, net of tax (less than)		(280)	$ 78	(1,004)	$ (11)
Revenue from Related Parties		1,900	2,700	4,100	5,200
Costs and Expenses, Related Party		2,900	2,900	5,700	5,500
Finite-Lived Intangible Assets, net	453,171	453,171		453,171		478,913
Escrow deposit	1,000,000	1,000,000		1,000,000		619,400
Reserves incorrect disposition of assets	21,100	21,100		21,100		22,200
Gain (Loss) on Investments		(4,353)	2,704	(3,418)	2,184
Other liabilities	157,522	157,522		157,522		132,043
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (102,530)	(102,530)		(102,530)		$ (122,418)
Income Tax Expense (Benefit)		$ 18,635	$ 20,283	24,909	36,062
Share-based compensation				$ 20,939	19,318
Mercury, Inc. [Member]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	45.00%	45.00%		45.00%
Payments to Acquire Equity Method Investments	$ 70,000
Calloptionremainininterst	55.00%	55.00%		55.00%
Call Option Fair Value	$ 4,600	$ 4,600		$ 4,600
Business Acquisition, Equity Interest Issued or Issuable, Basis for Determining Value	87000
Indefinite-lived Intangible Assets Acquired	$ 57,700
Finite-Lived Intangible Assets, net	$ 29,300	29,300		29,300
Estimated average life in years	15 years
RELS LLC [Member]
Pension and Other Postretirement Benefit Contributions	$ 13,500
Gain (Loss) on Investments		6,100
Other liabilities	9,200	9,200		9,200
Accumulated Other Comprehensive Income (Loss), Net of Tax	1,800	$ 1,800		$ 1,800
Minimum [Member]
Escrow deposits, period held by the Company (in business days)				2 days
Maximum [Member]
Equity in earnings/(losses) of affiliates, net of tax (less than)					$ 100
Escrow deposits, period held by the Company (in business days)				5 days
Sales Revenue, Net [Member]
Number of customers | customer			2		2
Ten Largest Clients [Member] | Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
Concentration risk, percentage		41.00%	43.00%	41.00%	43.00%
Client A [Member] | Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
Concentration risk, percentage		14.00%	15.00%	13.00%	14.00%
Client B [Member] | Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
Concentration risk, percentage		10.00%	11.00%	10.00%	12.00%
Misclassification Related To Liabilities [Member]
Accounts payable and accrued expenses	32,000	$ 32,000		$ 32,000
Other liabilities	$ (32,000)	$ (32,000)		$ (32,000)