Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 84,294	$ 54,437
Accounts receivable, net	2,874	2,548
Inventory	1,067	954
Prepaid expenses and other current assets	2,058	2,231
Total current assets	90,293	60,170
Property and equipment, net	8,934	10,151
Restricted cash	1,764	1,764
Operating lease assets	6,269	6,655
Total assets	107,260	78,740
Current liabilities:
Accounts payable	2,650	3,268
Accrued expenses and other current liabilities	5,769	7,635
Operating lease liabilities	1,238	1,126
Notes payable, net of discount, current	4,146
Total current liabilities	13,803	12,029
Operating lease liabilities, net of current portion	8,256	8,905
Derivative liability	32,535	12,124
Notes payable, net of discount	20,970	25,007
2026 convertible notes, net	26,352	24,305
Total liabilities	101,916	82,370
Commitments and contingencies (Note 12)
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 5,000,000 shares authorized and no shares issued or outstanding at June 30, 2020 and December 31, 2019
Common stock, $0.0001 par value; 100,000,000 shares authorized and 62,953,793 and 50,333,559 shares issued and outstanding at June 30, 2020 and December 31, 2019, respectively	6	5
Additional paid-in capital	447,033	379,980
Accumulated deficit	(441,695)	(383,615)
Total stockholders' equity (deficit)	5,344	(3,630)
Total liabilities and stockholders' equity (deficit)	$ 107,260	$ 78,740