Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 60,512	$ 76,000	$ 199,214	$ 224,493
Other comprehensive income (loss):
Foreign currency translation adjustments	7,379	(358)	29,951	5,567
Change in unrealized gain on investments, net of income tax provision (benefit) of $187, $(866), $868 and $1,445 for the three and nine months ended September 30, 2017 and 2016, respectively	310	(1,488)	1,438	2,424
Other comprehensive income (loss)	7,689	(1,846)	31,389	7,991
Comprehensive income	$ 68,201	$ 74,154	$ 230,603	$ 232,484