CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - UNAUDITED - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 11,581	$ 10,837	$ 31,818	$ 32,341
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	5,225	(7,938)	9,564	(9,040)
Unrealized holding gains (losses) on short-term investments arising during period	103	(254)	147	657
Other comprehensive income (loss), net of tax	5,328	(8,192)	9,711	(8,383)
Total comprehensive income, net of tax	$ 16,909	$ 2,645	$ 41,529	$ 23,958