Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 11,033	$ 50,805
Accounts receivable	2,825	1,786
Prepaid expenses and other current assets	1,438	1,340
Inventories	3,599	2,677
Total current assets	18,895	56,608
Property and equipment, net	5,845	7,315
Operating lease right-of-use assets	3,360
Restricted cash	180	180
Other assets	206	206
Total assets	28,486	64,309
Current liabilities:
Notes payable	42,902	42,373
Accounts payable	3,753	744
Accrued expenses and other current liabilities	11,207	6,073
Derivative liability	2,425	2,142
Deferred revenue	285	697
Current portion of lease incentives		268
Total current liabilities	60,572	52,297
Lease incentives, net of current portion		492
Operating lease liabilities, net of current portion	1,873
Deferred revenue, net of current portion	46	133
Commitments and contingencies (see Notes 12 and 13)
Stockholders’ (deficit) equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.001 par value; 200,000,000 shares authorized; 50,651,535 and 44,175,441 shares issued and outstanding at December 31, 2019 and December 31, 2018, respectively	51	44
Additional paid-in capital	342,121	328,514
Accumulated deficit	(376,177)	(317,171)
Total stockholders’ (deficit) equity	(34,005)	11,387
Total liabilities and stockholders’ (deficit) equity	$ 28,486	$ 64,309