CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Other Comprehensive Income [Abstract]
Net income	$ 14,133	$ 7,584	$ 26,355	$ 13,729
Other comprehensive income (loss), net of tax
Foreign currency translation		4		6
Change in fair value of marketable securities	25	39	(59)	163
Adjustment for net losses realized and included in net income				10
Total change in unrealized gains (losses) on marketable securities	25	39	(59)	173
Other comprehensive income (loss)	25	43	(59)	179
Comprehensive income	$ 14,158	$ 7,627	$ 26,296	$ 13,908