Condensed Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current assets
Cash and cash equivalents	$ 53,964	$ 7,942
Prepaid expenses and other current assets	443	88
Total current assets	54,407	8,030
Property and equipment, net	708	759
Restricted cash	94	94
Other assets	18	2,354
Total assets	55,227	11,237
Current liabilities:
Accounts payable	3,070	1,746
Accrued expenses	457	850
Notes payable, current portion	1,642	1,642
Deferred revenue, current portion	1,134	1,115
Total current liabilities	6,303	5,353
Deferred revenue, net of current portion	223	355
Restricted stock liability	8	10
Notes payable, net of current portion	2,466	2,876
Warrant liability		297
Commitments and contingencies
Stockholders' equity (deficit):
Common stock, $0.001 par value; 200,000,000 and 77,688,009 shares authorized at March 31, 2014 and December 31, 2013, respectively, and 16,037,232 and 1,636,137 shares issued and outstanding at March 31, 2014 and December 31, 2013, respectively	16	2
Additional paid-in capital	111,027	3,260
Accumulated deficit	(64,816)	(57,594)
Total stockholders' equity (deficit)	46,227	(54,332)
Total liabilities, convertible preferred stock, and stockholders' equity (deficit)	55,227	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