CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - UNAUDITED - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 14,014	$ 20,237
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	7,710	4,339
Unrealized holding gains (losses) on short-term investments arising during period	(94)	44
Other comprehensive income, net of tax	7,616	4,383
Total comprehensive income, net of tax	$ 21,630	$ 24,620