Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 48,152	$ 54,437
Accounts receivable, net	3,429	2,548
Inventory	1,107	954
Prepaid expenses and other current assets	2,465	2,231
Total current assets	55,153	60,170
Property and equipment, net	9,473	10,151
Restricted cash	1,764	1,764
Operating lease assets	6,467	6,655
Total assets	72,857	78,740
Current liabilities:
Accounts payable	2,839	3,268
Accrued expenses and other current liabilities	5,018	7,635
Operating lease liabilities	1,181	1,126
Notes payable, net of discount, current	2,074
Total current liabilities	11,112	12,029
Operating lease liabilities, net of current portion	8,590	8,905
Derivative liability	15,528	12,124
Notes payable, net of discount	22,987	25,007
2026 convertible notes, net	25,299	24,305
Total liabilities	83,516	82,370
Commitments and contingencies (Note 12)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized and no shares issued or outstanding at March 31, 2020 and December 31, 2019, respectively
Common stock, $0.0001 par value; 100,000,000 shares authorized and 53,037,703 and 50,333,559 shares issued and outstanding at March 31, 2020 and December 31, 2019, respectively	5	5
Additional paid-in capital	394,463	379,980
Accumulated deficit	(405,127)	(383,615)
Total stockholders’ deficit	(10,659)	(3,630)
Total liabilities and stockholders’ deficit	$ 72,857	$ 78,740