Income Taxes - Schedule of Significant Components of Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets (liabilities)
License and technology payments	$ 7,116	$ 7,221
Share-based compensation	22,131	20,342
Accrued expenses	362	371
Right-of-use asset	(163)
Lease obligation	162
Depreciation	(18)	(28)
Federal and state net operating loss carryforwards	105,375	88,766
Research and development credits	7,353	5,933
Other	6	5
Deferred income tax assets	142,324	122,610
Valuation allowance	(142,324)	(122,610)
Net deferred tax assets	$ 0	$ 0