Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 29,135,895	$ 36,205,559
Marketable securities	71,636,172	70,698,640
Prepaid expenses and other current assets	1,723,511	669,155
Total current assets	102,495,578	107,573,354
Property and equipment, net	590,179	553,294
Restricted cash	112,410	112,410
Total assets	103,198,167	108,239,058
Current liabilities:
Accounts payable	3,152,445	4,342,480
Accrued expenses and other current liabilities	1,425,038	2,578,269
Deferred revenue	7,500,000
Deferred rent	40,254	38,359
Total current liabilities	12,117,737	6,959,108
Loans payable, net	1,719,667	1,692,884
Capital lease, net of current portion	10,023	10,677
Deferred rent, net of current portion	271,291	281,885
Deferred revenue, net of current portion	1,875,000
Warrant liability	91,264	82,851
Other long term liabilities	19,151	8,025
Total liabilities	16,104,133	9,035,430
Commitments and contingencies (Note 6)
Stockholders' equity:
Common stock, $0.001 par value; 100,000,000 shares authorized, 39,347,565 and 39,241,173 shares issued and outstanding at March 31, 2015 and December 31, 2014, respectively	39,347	39,241
Additional paid-in capital	231,946,082	231,152,894
Accumulated deficit	(144,899,370)	(131,969,725)
Accumulated other comprehensive gain (loss)	7,975	(18,782)
Total stockholders' equity	87,094,034	99,203,628
Total liabilities and stockholders' equity	$ 103,198,167	$ 108,239,058