Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 65,295	$ 73,849
Accounts receivable	88	201
Prepaid expenses and other current assets	686	1,076
Inventories	252	115
Restricted cash	80	80
Total current assets	66,401	75,321
Property and equipment, net	5,332	2,760
Restricted cash, net of current portion	260	260
Deferred tax assets	313	313
Other assets	468	480
Total assets	72,774	79,134
Current liabilities:
Accounts payable	1,173	735
Accrued expenses	3,426	3,662
Notes payable	300	295
Deferred revenue	2,029	80
Deferred tax liabilities	313	313
Lease incentives	214	87
Total current liabilities	7,455	5,172
Notes payable, net of current portion	20,592	20,660
Lease incentives, net of current portion	995	106
Other liabilities	252	195
Commitments and contingencies (Note 13)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.001 par value; 200,000,000 at March 31, 2015 and December 31, 2014, respectively; 20,198,969 and 20,041,645 shares issued and outstanding at March 31, 2015 and December 31, 2014, respectively	20	20
Additional paid-in capital	157,673	156,576
Accumulated deficit	(114,213)	(103,595)
Total stockholders' equity	43,480	53,001
Total liabilities and stockholders' equity	$ 72,774	$ 79,134