Income Taxes - Schedule of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Net operating losses	$ 103,187	$ 87,142
Capitalized research and development	1,537	2,155
Accrued expenses	1,300	1,310
Research and development credits	5,343	5,282
Amortization	528	630
Depreciation	0	163
Deferred Tax Assets, Stock-based Compensation	5,868	4,334
Other, net	775	98
Total deferred tax assets	118,538	101,114
Less valuation allowance	(118,064)	(101,114)
Net deferred tax assets	474	0
IPR&D	(17,425)	(17,425)
Depreciation	(474)	0
Total deferred tax liabilities	(17,899)	(17,425)
Net deferred tax liability	$ (17,425)	$ (17,425)