Basis of Condensed Consolidated Financial Statements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Accounts payable and other accrued expenses	$ 171,030			$ 145,655
(Benefit)/provision for income taxes	(711)	$ 6,274
Deferred income tax assets and other current assets	600			400
Equity in earnings/(losses) of affiliates, net of tax (less than)	233	(723)
Tax escrow deposits	6,100,000			961,500
Reserves incorrect disposition of assets	20,600			21,700
Reclassification from AOCI to retained earnings for tax act	400
Revenue from related parties	300	2,200
Costs and Expenses, Related Party	3,300	2,800
Possible indemnification exposure, maximum	25,000
Gain related to legal settlement		$ 4,500
Accumulated other comprehensive loss	(93,384)		$ (93,700)	(93,691)
Disposal group, liabilities current	1,800			1,800
Contract costs	$ 1,600
Minimum
Escrow deposits, period held by the Company (in business days)	2 days
Maximum
Escrow deposits, period held by the Company (in business days)	5 days
Ten Largest Clients | Sales Revenue, Net | Customer Concentration Risk
Concentration risk, percentage	34.00%	40.00%
Client A | Sales Revenue, Net | Customer Concentration Risk
Concentration risk, percentage		12.00%
Accounts Payable and Accrued Liabilities
Reserves incorrect disposition of assets	$ 9,300			$ 9,400