Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets
Cash and cash equivalents	$ 3,217	$ 18,409
Marketable securities		3,260
Accounts and other receivables	1,865	140
Prepaid expenses and other current assets	1,552	1,912
Total current assets	6,634	23,721
Property and equipment, net	1,471	1,753
Operating lease right-of-use assets	1,537
Restricted cash	338	710
Other long-term assets	527	562
Total assets	10,507	26,746
Liabilities and stockholders’ deficit
Accounts payable and accrued expenses	4,911	8,342
Current portion of convertible notes		3,333
Current portion of capital lease obligation		214
Current portion of operating lease liabilities	284
Other current liabilities	236	115
Total current liabilities	5,431	12,004
Convertible notes, less current portion, net	77,343	78,105
Derivative and warrant liability	120	2,118
Capital lease obligation, less current portion		396
Operating lease liabilities, less current portion	1,901
Other long-term liabilities	168	689
Total liabilities	84,963	93,312
Commitments and contingencies (Note H)
Stockholders' deficit:
Common stock, $0.0001 par value, 250,000,000 shares authorized, 36,350,785 shares issued and outstanding as of December 31, 2019; 26,455,352 shares issued and outstanding as of December 31, 2018	4	3
Additional paid-in capital	171,254	154,623
Accumulated deficit	(245,714)	(221,192)
Total stockholders' deficit	(74,456)	(66,566)
Total liabilities and stockholders' deficit	10,507	26,746
Series A Convertible Preferred Stock [Member]
Stockholders' deficit:
Preferred stock
Series B-1 Convertible Preferred Stock [Member]
Stockholders' deficit:
Preferred stock
Series B-2 Convertible Preferred Stock [Member]
Stockholders' deficit:
Preferred stock
Undesignated Preferred Stock [Member]
Stockholders' deficit:
Preferred stock