Consolidated Statements of Comprehensive (Loss) Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (55,489)	$ (37,966)	$ 17,859
Unrealized gain (loss) on available-for-sale securities	516	(79)	(69)
Comprehensive (loss) income	$ (54,973)	$ (38,045)	$ 17,790