Income Taxes - Significant Components of Deferred Tax Assets and Tax Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carry-forwards	$ 268,173	$ 114,932
Stock-based compensation	43,978	33,138
Capitalized licenses, R&D and start-up costs	19,891	22,143
Tax credit carry-forwards	77,222	53,617
Accrued expenses	7,377	16,443
Deferred revenue	53,475	71,209
Operating lease liabilities	26,571
Lease financing obligation	10,570
Lease financing obligation		9,149
Other	11	2,870
Total gross deferred tax assets	507,268	323,501
Less: valuation allowance	(470,753)	(308,273)
Total deferred tax assets, net of valuation allowance	36,515	15,228
Deferred tax liabilities:
Financing right-of-use assets	(2,612)
Operating right-of-use assets	(24,944)
Fixed assets	(8,959)	(15,228)
Total deferred tax liabilities	(36,515)	(15,228)
Net deferred tax assets	$ 0	$ 0