Condensed Balance Sheets (USD $)	Sep. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 49,667,984	$ 21,215,228
Available for sale securities	68,670,000	11,341,000
Accounts receivable	57,000	135,000
Prepaid expenses and other current assets	1,445,000	740,000
Total current assets	119,840,000	33,431,000
Property and equipment, net	204,894	30,366
Deferred offering costs		1,079,000
Other assets	125,000	125,000
Total assets	120,170,000	34,665,000
Current liabilities:
Accounts payable	3,032,000	714,000
Accrued expenses	3,490,287	3,187,761
Total current liabilities	6,522,000	3,902,000
Other liabilities	34,000	8,000
Total liabilities	6,556,000	3,910,000
Redeemable convertible preferred stock; $0.00001 par value; 0 and 5,500,636 shares authorized at September 30, 2014 and December 31, 2013, respectively:
Redeemable convertible preferred stock		157,827,000
Stockholders' equity (deficit):
Common stock: $0.00001 par value; 175,000,000 and 14,700,000 authorized at September 30, 2014 and December 31, 2013, respectively; 20,300,243 and 1,383,345 shares issued and outstanding at September 30, 2014 and December 31, 2013, respectively
Additional paid-in capital	204,048,000
Treasury Stock, at cost, 2,553 shares	(79,000)
Accumulated other comprehensive loss	(51,257)	0
Accumulated deficit	(90,303,000)	(127,072,000)
Total stockholders' equity (deficit)	113,614,000	(127,072,000)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	120,170,000	34,665,000
Series A redeemable convertible preferred stock
Redeemable convertible preferred stock; $0.00001 par value; 0 and 5,500,636 shares authorized at September 30, 2014 and December 31, 2013, respectively:
Redeemable convertible preferred stock		39,367,000
Series B redeemable convertible preferred stock
Redeemable convertible preferred stock; $0.00001 par value; 0 and 5,500,636 shares authorized at September 30, 2014 and December 31, 2013, respectively:
Redeemable convertible preferred stock		21,257,000
Series C redeemable convertible preferred stock
Redeemable convertible preferred stock; $0.00001 par value; 0 and 5,500,636 shares authorized at September 30, 2014 and December 31, 2013, respectively:
Redeemable convertible preferred stock		$ 97,203,000