Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 54,059	$ 7,942
Prepaid expenses and other current assets	342	88
Total current assets	54,401	8,030
Property and equipment, net	486	759
Restricted cash	94	94
Other assets	19	2,354
Total assets	55,000	11,237
Current liabilities:
Accounts payable	2,458	1,746
Accrued expenses	1,987	850
Notes payable, current portion	251	1,642
Deferred revenue, current portion	506	1,115
Total current liabilities	5,202	5,353
Deferred revenue, net of current portion		355
Restricted stock liability	4	10
Notes payable, net of current portion	9,749	2,876
Warrant liability	3,219	297
Commitments and contingencies (Note 7)
Stockholders' equity (deficit):
Preferred stock, $0.001 par value per share; 5,000,000 and no shares authorized at December 31, 2014 and 2013, respectively, and no shares issued and outstanding at December 31, 2014 and 2013
Common stock, $0.001 par value per share; 200,000,000 and 77,688,009 shares authorized at December 31, 2014 and 2013, respectively, and 17,933,260 and 1,636,137 shares issued and outstanding at December 31, 2014 and 2013, respectively	18	2
Additional paid-in capital	128,558	3,260
Accumulated deficit	(91,750)	(57,594)
Total stockholders' equity (deficit)	36,826	(54,332)
Total liabilities, convertible preferred stock, and stockholders' equity (deficit)	55,000	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