Condensed Consolidated Statements of Comprehensive Income (Loss ) (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (8,393)	$ 16,429	$ (24,080)	$ 13,849
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities	2	(1)	1	(1)
Comprehensive income (loss)	$ (8,391)	$ 16,428	$ (24,079)	$ 13,848