Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 79,425	$ 83,983	$ 250,276	$ 241,616
Other comprehensive loss, net of tax:
Foreign currency translation adjustments	(6,037)	(6,308)	(10,290)	(4,896)
Unrealized (loss) gain on investments:
Unrealized (losses) gains during the period, net of income taxes of $200, $330, $501 and $(426)	(734)	(584)	(1,254)	407
Less: reclassification adjustment for losses (gains) realized in net income, net of income taxes of $(62), $(39), $(49) and $(1)	117	76	93	7
Unrealized (loss) gain on investments:	(617)	(508)	(1,161)	414
Total other comprehensive loss, net of tax	(6,654)	(6,816)	(11,451)	(4,482)
Comprehensive income	$ 72,771	$ 77,167	$ 238,825	$ 237,134