Income Taxes - Schedule of principal components of the company's deferred tax assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
NOL carryforwards	$ 243,063	$ 225,285
Capitalized research and development	4,099	3,919
Research and development credits	9,608	8,380
Interest Expense	2,729	1,125
Accrued expenses	5,342	2,644
Stock-based compensation	14,952	14,377
UNICAP	103	86
Allowance for bad debt	1,832	840
Operating lease liability	1,696
Other	119	106
Gross non-current deferred tax assets	283,543	256,762
Valuation allowance	(255,242)	(228,322)
Net non-current deferred tax assets	28,301	28,440
Deferred tax liabilities:
Depreciation	(216)	(347)
Right-of-Use asset	(1,677)
Convertible debt	(26,408)	(28,093)
Gross non-current deferred tax liabilities	(28,301)	(28,440)
Net non-current deferred tax assets (liabilities)	$ 0	$ 0