Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 15,140	$ 17,651	$ 11,996
Other comprehensive income (loss), net of taxes:
Foreign currency translation	5,593	(2,764)	(3,187)
Net change in market value of investments	(32)	17	(26)
Other comprehensive income (loss)	5,561	(2,747)	(3,213)
Comprehensive income	$ 20,701	$ 14,904	$ 8,783