CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - UNAUDITED - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 15,117	$ 11,581	$ 29,131	$ 31,818
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	(16,231)	5,225	(8,521)	9,564
Unrealized holding gains (losses) on short-term investments arising during period	68	103	(26)	147
Other comprehensive income (loss), net of tax	(16,163)	5,328	(8,547)	9,711
Total comprehensive income (loss), net of tax	$ (1,046)	$ 16,909	$ 20,584	$ 41,529