Consolidated Balance Sheets (USD $)	Dec. 31, 2012	Dec. 31, 2011
Assets
Cash and cash equivalents	$ 45,511,641	$ 17,707,476
Investment securities, available-for-sale	64,682,270	0
Prepaid expenses and other current assets	1,584,308	1,196,618
Total current assets	111,778,219	18,904,094
Fixed assets, net	148,838	311,366
Security deposits	251,540	254,869
Total assets	112,178,597	19,470,329
Liabilities and Stockholders' Equity (Deficit)
Accounts payable, accrued expenses and other liabilities	3,745,773	1,504,198
Short-term portion of warrant liability	7,596,659	0
Short-term portion of deferred revenue	1,621,622	2,446,107
Short-term portion of capital leases	0	81,762
Total current liabilities	12,964,054	4,032,067
Long-term liabilities:
Long-term portion of deferred revenue	10,540,543	12,162,163
Long-term portion of warrant liability	22,762,135	5,835,877
Total liabilities	46,266,732	22,030,107
Stockholders' equity (deficit):
Common stock. Authorized 65,000,000 shares and issued and outstanding 3,329,666 shares as of December 31, 2011; 25,000,000 shares authorized and 16,526,885, shares issued and outstanding as of December 31, 2012; par value $0.001 per share	16,527	3,330
Additional paid-in capital	184,100,139	72,133,893
Accumulated other comprehensive loss, net	(21,451)	(184,500)
Accumulated deficit during development stage	(118,183,350)	(74,540,279)
Total stockholders' equity (deficit)	65,911,865	(2,559,778)
Total liabilities and stockholders' equity (deficit)	112,178,597	19,470,329
Series A Preferred Stock [Member]
Stockholders' equity (deficit):
Preferred stock	0	13,889
Total stockholders' equity (deficit)	0	13,889
Series B Preferred Stock [Member]
Stockholders' equity (deficit):
Preferred stock	0	13,889
Total stockholders' equity (deficit)	$ 0	$ 13,889