Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 86,240	$ 82,813	$ 170,851	$ 157,633
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	4,530	3,378	(4,253)	1,412
Unrealized (loss) gain on investments:
Unrealized (losses) gains during the period, net of income taxes of $326, $(461), $301 and $(756)	(527)	453	(520)	991
Less: reclassification adjustment for losses (gains) realized in net income, net of income taxes of $(39), $13, $13 and $38	70	(24)	(24)	(69)
Unrealized (loss) gain on investments:	(457)	429	(544)	922
Total other comprehensive income (loss), net of tax	4,073	3,807	(4,797)	2,334
Comprehensive income	$ 90,313	$ 86,620	$ 166,054	$ 159,967