Balance Sheets - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 36,802,778	$ 46,773,566
Marketable securities	107,707,828	125,864,447
Prepaid expenses and other current assets	3,129,866	1,892,217
Total current assets	147,640,472	174,530,230
Property and equipment, net	807,353	696,280
Restricted cash	112,620	112,620
Intangible asset, net	13,906	14,844
Total assets	148,574,351	175,353,974
Current liabilities:
Accounts payable	4,925,372	6,749,625
Accrued expenses and other current liabilities	3,785,223	3,029,782
Deferred revenue		3,750,000
Deferred rent	48,086	43,907
Total current liabilities	8,758,681	13,573,314
Loans payable, net	18,249,810	18,185,898
Capital leases, net of current portion	13,176	7,942
Deferred rent, net of current portion	214,679	238,917
Warrant liability	83,517	153,238
Other long term liabilities	270,532	63,200
Total liabilities	27,590,395	32,222,509
Stockholders' equity:
Common stock—$0.001 par value; 100,000,000 shares authorized, 52,177,674 and 50,802,603 shares issued and outstanding at June 30, 2016 and December 31, 2015 respectively	52,178	50,802
Preferred stock - $0.001 par value; 5,000,000 shares authorized, none issued or outstanding at June 30, 2016 and December 31, 2015, respectively
Additional paid-in capital	340,349,923	325,784,484
Accumulated deficit	(219,493,262)	(182,497,965)
Accumulated other comprehensive loss	75,117	(205,856)
Total stockholders' equity	120,983,956	143,131,465
Total liabilities, redeemable convertible preferred stock and stockholders' equity	$ 148,574,351	$ 175,353,974