Income Taxes - Schedule of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Federal, state and foreign net operating loss carryforwards	$ 186,963	$ 134,009
Capitalized research and development	486	925
Accrued expenses	2,498	1,311
Research and development credits	5,343	5,343
Amortization	2,949	1,028
Lease liability	2,534	2,547
Stock-based compensation	7,878	6,464
Other, net	2,690	1,979
Total deferred tax assets	211,341	153,606
Less: valuation allowance	(176,594)	(151,544)
Total deferred tax assets, net of valuation allowance	34,747	2,062
Operating lease right-of-use asset	(1,585)	(1,640)
IPR&D	(15,857)	(17,425)
Discount on Notes	(17,305)	0
Depreciation	0
Depreciation		(422)
Total deferred tax liabilities	(34,747)	(19,487)
Total net deferred tax liabilities	$ 0	$ (17,425)