Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed Consolidated Statement of Comprehensive Income [Abstract]
Net income	$ 46,884	$ 66,730	$ 106,330	$ 112,850
Other comprehensive income (loss), net of income taxes:
Foreign currency translation adjustments	(1,580)	2,136	(1,448)	2,811
Unrealized gain (loss) on available-for-sale securities	108	(95)	49	(371)
Tax benefit (expense)	(26)	37	(68)	131
Other comprehensive income (loss), net of income taxes	(1,498)	2,078	(1,467)	2,571
Comprehensive income	$ 45,386	$ 68,808	$ 104,863	$ 115,421