Statements of Cash Flows (Unaudited) (USD $)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities:
Net loss	$ (18,308,621)	$ (17,101,260)
Non-cash items included in net loss:
Depreciation and amortization	161,865	129,735
Change in fair value of common stock warrant liability	1,250,850	42,482
Stock-based compensation	850,990	892,894
Treasury shares issued for services and 401(k) matching contribution	94,189	116,188
Change in deferred rent liability	59,085
Net changes in:
Accrued interest on short term investments and other current assets	9,897	(259,666)
Accounts payable	(967,967)	(1,775,932)
Other accrued liabilities	683,575	(347,422)
Net cash used in operating activities:	(16,166,137)	(18,302,981)
Cash flows from investing activities:
Purchases of investment securities	(16,213,657)	(10,415,493)
Proceeds from sale and maturity of investment securities	12,287,030	395,556
Security deposit on letter of credit		(250,000)
Purchases of property and equipment	(381,110)	(328,866)
Net cash used in investing activities	(4,307,737)	(10,598,803)
Cash flows from financing activities:
Proceeds from sale of 8% Series A Redeemable, Convertible Preferred Stock, net of issuance costs		4,324,080
Proceeds from sale of common stock equity, net of issuance costs		34,268,411
Proceeds from notes payable	4,814,398
Proceeds from exercise of common stock warrants	3,823,690	394,336
Proceeds from exercise of options to purchase common stock	104,538
Principal payments on notes payable	(96,270)	(91,069)
Net cash provided by financing activities	8,646,356	38,895,758
(Decrease) increase in cash and cash equivalents	(11,827,518)	9,993,974
Cash and cash equivalents at beginning of period	20,145,854	1,138,916
Cash and cash equivalents at end of period	8,318,336	11,132,890
Supplemental disclosures of cash flow information:
Interest and preferred stock dividends paid	$ 187,995	$ 481,087