Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net loss before income taxes:
Net loss before income taxes	$ (232,566)	$ (146,863)	$ (98,866)
Current:
United States	3	(24)	193
Other	0	0	0
Total	3	(24)	193
Deferred:
United States	0	(1,734)	0
Other	0	0	0
Total	0	(1,734)	0
Provision for income taxes	$ 3	$ (1,758)	$ 193
Effective tax rate (in percentage)	0.00%	1.20%	(0.19%)
United States
Net loss before income taxes:
Net loss before income taxes	$ (203,230)	$ (133,113)	$ (88,123)
Other
Net loss before income taxes:
Net loss before income taxes	$ (29,336)	$ (13,750)	$ (10,743)