CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 82,555	$ 51,367	$ 221,154	$ 142,061
Net change in foreign currency translation adjustment	884	(76)	1,624	(143)
Change in unrealized gains (losses) on investments, net of tax	60	(437)	102	1,038
Other comprehensive income (loss)	944	(513)	1,726	895
Comprehensive income	$ 83,499	$ 50,854	$ 222,880	$ 142,956