Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 321,406	$ 333,948	$ 293,487
Other comprehensive loss:
Foreign currency translation adjustments	(22,872)	(15,349)	(4,361)
Unrealized (losses) gains on investments, net of income tax benefit of $773, $689 and $457 for the years ended December 31, 2015, 2014 and 2013, respectively	(970)	(171)	3,910
Other comprehensive loss	(23,842)	(15,520)	(451)
Comprehensive income	$ 297,564	$ 318,428	$ 293,036