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	$ 101,739	$ 86,704	$ 282,245	$ 245,206
Other comprehensive gain (loss), net of tax:
Foreign currency translation adjustments	7,318	(3,053)	17,028	(5,704)
Unrealized gain (loss) on investments:
Unrealized gains (losses) during the period, net of income taxes of $(116), $94, $(148) and $(146)	294	(160)	435	190
Less: reclassification adjustment for losses realized in net income, net of income taxes of $(41), $(52), $(84) and $(143)	105	102	194	266
Unrealized gain (loss) on investments:	399	(58)	629	456
Total other comprehensive gain (loss), net of tax	7,717	(3,111)	17,657	(5,248)
Comprehensive income	$ 109,456	$ 83,593	$ 299,902	$ 239,958