Business Segment Information - Reconciliation of Segment Profit to Income Before Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reconciliation of segment profit to income before income taxes
Segment profit	$ 56,894	$ 53,167	$ 116,826	$ 118,114
Stock compensation expense	(9,510)	(13,795)	(18,397)	(27,696)
Changes in fair value of contingent consideration	(463)	(2,567)	(197)	(17,536)
Impairment of intangible assets	(4,800)		(4,800)
Non-controlling interest segment profit (loss)	(1,312)	(350)	(1,147)	(444)
Depreciation and amortization	(25,580)	(25,022)	(50,587)	(48,518)
Interest expense	(1,994)	(1,653)	(3,742)	(3,279)
Interest income	692	500	1,375	966
Income before income taxes	$ 13,927	$ 10,280	$ 39,331	$ 21,607