Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 423,201	$ 184,189	$ 121,102
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	672	(348)	(494)
Net change in unrealized gains (losses) on available-for-sale securities	(1,135)	(452)	153
Other comprehensive loss	(463)	(800)	(341)
Comprehensive income	$ 422,738	$ 183,389	$ 120,761