Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 22,869	$ (70,279)	$ (48,882)
Other comprehensive income (loss) (net of tax):
Net change in net unrealized loss on investments	(202)	(103)	(249)
Net change in unrealized gain (loss) on hedging instruments	1,225	(44)	407
Other comprehensive income (loss)	1,023	(147)	158
Comprehensive income (loss)	$ 23,892	$ (70,426)	$ (48,724)