Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 58,822	$ 73,488
Accounts receivable	409	327
Prepaid expenses and other current assets	931	820
Inventories, net	489	803
Total current assets	60,651	75,438
Property and equipment, net	14,468	13,589
Restricted cash	260	260
Other assets	280	281
Total assets	75,659	89,568
Current liabilities:
Accounts payable	1,161	962
Accrued expenses and other current liabilities	4,060	4,908
Current portion of notes payable	1,316	1,269
Deferred revenue	2,127	2,445
Current portion of lease incentives	249	301
Total current liabilities	8,913	9,885
Notes payable, net of current portion	39,750	39,504
Lease incentives, net of current portion	791	792
Other liabilities	175	49
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued and outstanding at March 31, 2017 and December 31, 2016	0	0
Common stock, $0.001 par value; 200,000,000 shares authorized; 30,594,342 and 30,482,712 shares issued and outstanding at March 31, 2017 and December 31, 2016, respectively	31	30
Additional paid-in capital	244,391	242,997
Accumulated deficit	(218,392)	(203,689)
Total stockholders’ equity	26,030	39,338
Total liabilities and stockholders’ equity	$ 75,659	$ 89,568