Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 73,488	$ 73,662
Accounts receivable	327	369
Prepaid expenses and other current assets	820	838
Inventories, net	803	683
Total current assets	75,438	75,552
Property and equipment, net	13,589	10,655
Restricted cash	260	260
Other assets	281	358
Total assets	89,568	86,825
Current liabilities:
Accounts payable	962	1,228
Accrued expenses and other current liabilities	4,908	4,162
Current portion of notes payable	1,269	4,449
Deferred revenue	2,445	2,146
Current portion of lease incentives	301	268
Total current liabilities	9,885	12,253
Notes payable, net of current portion	39,504	26,121
Lease incentives, net of current portion	792	1,076
Other liabilities	49	436
Commitments and contingencies (see Note 13)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued and outstanding at December 31, 2016 and December 31, 2015
Common stock, $0.001 par value; 200,000,000 shares authorized; 30,482,712 and 24,175,381 shares issued and outstanding at December 31, 2016	30	24
Additional paid-in capital	242,997	195,800
Accumulated deficit	(203,689)	(148,885)
Total stockholders' equity	39,338	46,939
Total liabilities and stockholders' equity	$ 89,568	$ 86,825