CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 100,872	$ 82,555	$ 302,843	$ 221,154
Net change in foreign currency translation adjustment	(1,756)	884	(1,473)	1,624
Change in unrealized gains (losses) on investments, net of tax	117	60	174	102
Other comprehensive (loss) income	(1,639)	944	(1,299)	1,726
Comprehensive income	$ 99,233	$ 83,499	$ 301,544	$ 222,880