Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 65,414	$ 54,062
Accounts receivable	1,114	201
Inventory	895	217
Prepaid expenses and other current assets	2,213	1,713
Total current assets	69,636	56,193
Property and equipment, net	10,474	10,236
Restricted cash	1,764	6,614
Operating lease assets	6,836
Total assets	88,710	73,043
Current liabilities:
Accounts payable	3,461	2,965
Accrued expenses and other current liabilities	6,471	6,194
Operating lease liabilities	1,073
Total current liabilities	11,005	9,159
Other liabilities		3,221
Operating lease liabilities, net of current portion	9,206
Derivative liability	9,100
Notes payable, net of discount	24,952	24,788
2026 convertible notes, net	23,146
Total liabilities	77,409	37,168
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 September 30, 2019 and December 31, 2018, respectively
Common stock, $0.0001 par value; 100,000,000 shares authorized and 48,079,615 and 41,518,091 shares issued and outstanding at September 30, 2019 and December 31, 2018	5	4
Additional paid-in capital	368,894	333,114
Accumulated deficit	(357,598)	(297,243)
Total stockholders' equity	11,301	35,875
Total liabilities and stockholders' equity	$ 88,710	$ 73,043