Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 81,005	$ 86,240	$ 158,502	$ 170,851
Other comprehensive (loss) gain, net of tax:
Foreign currency translation adjustments	(5,080)	4,530	(2,651)	(4,253)
Unrealized (loss) gain on investments:
Unrealized gains (losses) during the period, net of income taxes of $(49), $326, $(240) and $301	20	(527)	350	(520)
Less: reclassification adjustment for (gains) losses realized in net income, net of income taxes of $12, $(39), $(91) and $13	(23)	70	164	(24)
Unrealized (loss) gain on investments:	(3)	(457)	514	(544)
Total other comprehensive (loss) gain, net of tax	(5,083)	4,073	(2,137)	(4,797)
Comprehensive income	$ 75,922	$ 90,313	$ 156,365	$ 166,054