Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 53,714	$ 74,583
Other comprehensive income:
Foreign currency translation adjustments	6,282	9,927
Change in unrealized (loss) gain on investments, net of income tax benefit (provision) of $871 and $(488) for the three months ended March 31, 2018 and 2017, respectively	(2,686)	810
Other comprehensive income	3,596	10,737
Comprehensive income	$ 57,310	$ 85,320