Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net Income (loss)	$ (370)	$ (11,738)	$ 19,223	$ (60,461)
Other comprehensive gain (loss) (net of tax):
Net change in net unrealized gain (loss) on investments	55	(130)	105	76
Net change in unrealized gain (loss) on hedging instruments	(987)	224	1,161	486
Other comprehensive income (loss)	(932)	94	1,266	562
Comprehensive income (loss)	$ (1,302)	$ (11,644)	$ 20,489	$ (59,899)