CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - UNAUDITED - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 17,894	$ 16,747	$ 50,235	$ 38,899
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	(1,393)	(8,755)	(10,433)	(10,367)
Unrealized holding gains (losses) on short-term investments arising during period	(566)	(6)	91
Other comprehensive loss, net of tax	(1,959)	(8,761)	(10,342)	(10,367)
Total comprehensive income, net of tax	$ 15,935	$ 7,986	$ 39,893	$ 28,532