Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 16,466	$ 12,303
Marketable securities	52,048
Prepaid expenses and other current assets	1,380	334
Total current assets	69,894	12,637
Property and equipment, net	790	76
Other assets	252	45
Total assets	70,936	12,758
Current liabilities:
Accounts payable	1,309	300
Accrued expenses and other current liabilities	21,911	22,007
Current portion of note payable, net of discount	2,027	13,005
Total current liabilities	25,247	35,312
Note payable, net of current portion and discount	22,295
Warrant liability		1,945
Commitments and contingencies
Stockholders' deficit:
Common stock, $.0001 par value; 200,000,000 shares and 100,000,000 shares authorized, 29,747,797 shares and 385,664 shares issued and outstanding at September 30, 2014 and December 31, 2013, respectively	3
Additional paid-in-capital	349,677
Accumulated other comprehensive loss	(10)
Accumulated deficit	(326,276)	(277,301)
Total stockholders' deficit	23,394	(277,301)
Total liabilities, convertible preferred stock and stockholders' deficit	70,936	12,758
Series B Convertible Preferred Stock
Current liabilities:
Preferred Stock		43,892
Stockholders' deficit:
Total stockholders' deficit		43,892
Series A-1 Convertible Preferred Stock
Current liabilities:
Preferred Stock		78,737
Stockholders' deficit:
Total stockholders' deficit		78,737
Series A-2 Convertible Preferred Stock
Current liabilities:
Preferred Stock		93,977
Stockholders' deficit:
Total stockholders' deficit		93,977
Series A-3 Convertible Preferred Stock
Current liabilities:
Preferred Stock		12,232
Stockholders' deficit:
Total stockholders' deficit		12,232
Series A-4 Convertible Preferred Stock
Current liabilities:
Preferred Stock		271
Stockholders' deficit:
Total stockholders' deficit		271
Series A-5 Convertible Preferred Stock
Current liabilities:
Preferred Stock		525
Stockholders' deficit:
Total stockholders' deficit		525
Series A-6 Convertible Preferred Stock
Current liabilities:
Preferred Stock		23,168
Stockholders' deficit:
Total stockholders' deficit		$ 23,168