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	$ 218,321	$ 316,132	$ 321,406
Other comprehensive income (loss):
Foreign currency translation adjustments	34,698	(14,081)	(22,872)
Change in unrealized loss on investments, net of income tax benefit of $245, $432 and $773 for the years ended December 31, 2017, 2016 and 2015, respectively	(406)	(688)	(970)
Other comprehensive income (loss)	34,292	(14,769)	(23,842)
Comprehensive income	$ 252,613	$ 301,363	$ 297,564