Balance Sheets - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 39,034,709	$ 36,205,559
Marketable securities	129,937,375	70,698,640
Prepaid expenses and other current assets	986,875	669,155
Total current assets	169,958,959	107,573,354
Property and equipment, net	601,476	553,294
Restricted cash	112,410	112,410
Total assets	170,672,845	108,239,058
Current liabilities:
Accounts payable	2,360,667	4,342,480
Accrued expenses and other current liabilities	2,670,607	2,578,269
Deferred revenue	5,625,000
Deferred rent	41,818	38,359
Total current liabilities	10,698,092	6,959,108
Loan payable, net	1,777,667	1,692,884
Capital lease, net of current portion	8,642	10,677
Deferred rent, net of current portion	250,841	281,885
Warrant liability	153,953	82,851
Other long term liabilities	40,430	8,025
Total liabilities	$ 12,929,625	$ 9,035,430
Commitments and contingencies (Note 6)
Stockholders' equity:
Common stock, $0.001 par value; 100,000,000 shares authorized, 50,736,251 and 39,241,173 shares issued and outstanding at September 30, 2015 and December 31, 2014, respectively	$ 50,736	$ 39,241
Additional paid-in capital	324,683,788	231,152,894
Accumulated deficit	(167,033,704)	(131,969,725)
Accumulated other comprehensive income (loss)	42,400	(18,782)
Total stockholders' equity	157,743,220	99,203,628
Total liabilities and stockholders' equity	$ 170,672,845	$ 108,239,058