Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 57,772	$ 73,635	$ 138,702	$ 148,493
Other comprehensive income (loss):
Foreign currency translation adjustments	13,073	(3,728)	22,572	5,925
Change in unrealized gain on investments, net of income tax provision of $193, $529, $681 and $2,311 for the three and six months ended June 30, 2017 and 2016, respectively	320	904	1,130	3,912
Other comprehensive income (loss)	13,393	(2,824)	23,702	9,837
Comprehensive income	$ 71,165	$ 70,811	$ 162,404	$ 158,330