Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net loss	$ (67,323)	$ (72,859)	$ (142,698)	$ (144,689)
Change in net unrealized gain (loss) on available-for-sale investments, net of tax	1,172	981	3,269	(614)
Comprehensive loss	$ (66,151)	$ (71,878)	$ (139,429)	$ (145,303)