Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net loss	$ (80,000)	$ (110,286)	$ (218,651)	$ (229,918)
Other comprehensive income (loss):
Net unrealized gain on available-for-sale investments	7,688	2,197	2,567	6,882
Net foreign currency translation gain (loss)	(96)	108	(847)	143
Other comprehensive income	7,592	2,305	1,720	7,025
Comprehensive loss	$ (72,408)	$ (107,981)	$ (216,931)	$ (222,893)