Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 12,620	$ 15,256
Restricted cash, current portion	59	1,092
Short-term investments	106,247	130,860
Accounts receivable, net of allowance of $2,000 in 2017 and $1,890 in 2016	8,252	13,396
Inventory	8,998	6,414
Prepaid expenses and other current assets	8,612	7,097
Total current assets	144,788	174,115
Property and equipment, net	29,667	32,289
Restricted cash, long term portion	342	342
Other assets	3,979	3,934
Total assets	178,776	210,680
Current liabilities:
Accounts payable	8,529	11,479
Accrued compensation	9,599	11,067
Other accrued liabilities	33,207	19,879
Deferred revenue	1,420	574
Short-term debt financing	50,112	49,624
Warrants	2,644	3,792
Total current liabilities	105,511	96,415
Long-term debt financing	73,065
Deferred rent, net of current portion	9,241	7,789
Other long-term liabilities	1,329
Total liabilities	189,146	104,204
Commitments and contingencies (Note 6)
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value: 50,000 shares authorized; no shares issued and outstanding at December 31, 2017 and 2016, respectively
Common stock, $0.0001 par value: 750,000 shares authorized at December 31, 2017 and 2016, respectively; 54,040 and 52,665 shares issued and outstanding at December 31, 2017 and 2016, respectively	6	5
Additional paid in capital	472,552	453,044
Accumulated deficit	(482,162)	(345,848)
Accumulated other comprehensive loss	(766)	(725)
Total stockholders' (deficit) equity	(10,370)	106,476
Total liabilities and stockholders' equity (deficit)	$ 178,776	$ 210,680