Basis of Condensed Consolidated Financial Statements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019	Dec. 31, 2018
Revenue from related parties		$ 300		$ 600
Costs and Expenses, Related Party	$ 500	2,000	$ 700	5,300
Possible indemnification exposure, maximum	25,000		25,000
Deferred income tax assets and other current assets	600		600
Disposal group, liabilities current	2,100		2,100			$ 2,200
Tax escrow deposits	754,200		754,200			696,000
Reserves incorrect disposition of assets	20,600		20,600			21,200
Increase/(decrease) in contingent consideration value	(600)	(1,500)	(200)	(1,100)
Operating	61,910		61,910		$ 67,700	0
Total	96,741		96,741		$ 103,900
Restricted cash included in other assets	11,662	9,756	11,662	9,756		9,967
Restricted cash included in prepaid expenses and other current assets	2,024	$ 1,070	$ 2,024	$ 1,070		3,012
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
Accounts Payable and Accrued Liabilities
Reserves incorrect disposition of assets	$ 9,300		$ 9,300			$ 9,200
Ten Largest Clients | Sales Revenue, Net | Customer Concentration Risk
Concentration risk, percentage	30.00%	32.00%	29.00%	33.00%