Condensed Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 35,943	$ 7,942
Prepaid expenses and other current assets	348	88
Total current assets	36,291	8,030
Property and equipment, net	585	759
Restricted cash	94	94
Other assets	11	2,354
Total assets	36,981	11,237
Current liabilities:
Accounts payable	2,588	1,746
Accrued expenses	1,656	850
Notes payable, current portion	1,642	1,642
Deferred revenue, current portion	621	1,115
Total current liabilities	6,507	5,353
Deferred revenue, net of current portion	45	355
Restricted stock liability	6	10
Notes payable, net of current portion	1,645	2,876
Warrant liability		297
Commitments and contingencies
Stockholders' equity (deficit):
Preferred stock, $0.001 par value per share; 5,000,000 shares and none authorized at September 30, 2014 and December 31, 2013, respectively, and none issued and outstanding at September 30, 2014 and December 31 2013
Common stock, $0.001 par value; 200,000,000 and 77,688,009 shares authorized at September 30, 2014 and December 31, 2013, respectively, and 16,134,515 and 1,636,137 shares issued and outstanding at September 30, 2014 and December 31, 2013, respectively	16	2
Additional paid-in capital	112,373	3,260
Accumulated deficit	(83,611)	(57,594)
Total stockholders' equity (deficit)	28,778	(54,332)
Total liabilities, convertible preferred stock, and stockholders' equity (deficit)	36,981	11,237
Series A Convertible Preferred Stock [Member]
Current liabilities:
Convertible preferred stock, value		45,035
Series B Convertible Preferred Stock [Member]
Current liabilities:
Convertible preferred stock, value		$ 11,643