Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 89,248	$ 3,618
Short-term investments	29,117
Prepaid expenses and other current assets	859	52
Total current assets	119,224	3,670
Property and equipment, net	756
Other assets	144	1,850
Total assets	120,124	5,520
Current liabilities:
Accounts payable	1,709	1,146
Accrued expenses and other current liabilities	1,534	992
Notes payable, current portion		3,063
Convertible Bridge Notes		1,541
Convertible Bridge Notes redemption rights derivative		480
Total current liabilities	3,243	7,222
Notes payable, net of current portion		2,550
Warrant liabilities		482
Other long-term liabilities	406	24
Total liabilities	$ 3,649	10,278
Redeemable convertible preferred stock		$ 46,801
Commitments and Contingencies (Note 7)
Stockholders' equity (deficit):
Preferred Stock, $0.001 par value: 5,000,000 shares authorized and 0 shares issued or outstanding
Common stock, $0.01 par value: 120,000,000 shares and 43,509,727 shares authorized at September 30, 2015 and December 31, 2014, respectively; 26,410,251 shares and 1,020,088 shares issued and outstanding at September 30, 2015 and December 31, 2014, respectively	$ 264	$ 10
Additional paid-in capital	304,062	76,472
Accumulated deficit	(187,851)	(128,041)
Total stockholders' equity (deficit)	116,475	(51,559)
Total Liabilities, Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit)	$ 120,124	5,520
Series AA Redeemable Convertible Preferred Stock [Member]
Current liabilities:
Redeemable convertible preferred stock		46,253
Series X Redeemable Convertible Preferred Stock [Member]
Current liabilities:
Redeemable convertible preferred stock		$ 548