CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - UNAUDITED - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 20,237	$ 21,504
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	4,339	(1,102)
Unrealized holding gains on short-term investments arising during period	44	911
Other comprehensive income (loss), net of tax	4,383	(191)
Total comprehensive income, net of tax	$ 24,620	$ 21,313