Condensed Consolidated Statements of Comprehensive (Loss) Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (9,781)	$ 23,083
Other comprehensive (loss) gain, net of tax:
Net change in net unrealized (loss) gain on investments	(396)	28
Net change in unrealized (loss) gain on hedging instruments	(411)	1,729
Total other comprehensive (loss) income, net of tax	(807)	1,757
Comprehensive (loss) income	$ (10,588)	$ 24,840