CONSOLIDATED STATEMENTS OF INCOME (Parenthetical) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CONSOLIDATED STATEMENTS OF INCOME
Stock compensation expense	$ 9,849	$ 9,176	$ 9,510	$ 8,887	$ 9,791	$ 12,897	$ 13,795	$ 13,901	$ 37,422	$ 50,384	$ 40,584
changes in fair value of contingent consideration	$ (614)	$ 313	463	$ (266)	$ (3,017)	$ 29,738	$ 2,567	$ 14,969	(104)	$ 44,257	$ 6,172
Impairment of intangible assets			$ 4,800						$ 4,800