Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net loss	$ (39,118)	$ (65,495)	$ (168,700)	$ (208,193)
Change in net unrealized gain (loss) on available-for-sale investments	(1,197)	107	3,934	3,376
Comprehensive loss	$ (40,315)	$ (65,388)	$ (164,766)	$ (204,817)