STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended		103 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012
Cash flows from operating activities:
Net loss	$ (24,470)	$ (39,008)	$ (212,062)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	118	37	2,034
Stock-based compensation	1,212	702	16,513
Change in fair value of warrants	5,811	11,080	1,090
Loss on disposal of fixed assets			9
Common stock issued in exchange for in-process research and development		17,457	17,457
(Increase) decrease in:
Collaboration receivable	79	(5,000)
Prepaid expenses and other current assets	(9,490)	(510)	(10,803)
Other noncurrent assets	(23)	7	(794)
Deposits		(4)	(91)
Increase (decrease) in:
Accounts payable	257	822	1,984
Accrued expenses	713	1,324	11,534
Deferred revenue	(200)	4,933	4,133
Deferred rent	133	(7)	328
Net cash used in operating activities	(25,860)	(8,167)	(168,668)
Cash flows from investing activities:
Purchases of property and equipment	(154)	(227)	(3,221)
Proceeds from sale of property and equipment			1
Net cash used in investing activities	(154)	(227)	(3,220)
Cash flows from financing activities:
Stockholders' capital contribution			500
Proceeds from exercise of stock options		724	1,343
Payments to employees for repurchase of common stock		(78)	(2,321)
Proceeds from exercise of warrants	140	186	12,889
Proceeds from issuance of common stock and warrants, net	49,169	71,207	270,725
Proceeds from issuance of preferred stock, net			16,760
Net cash provided by financing activities	49,309	72,039	299,896
Net increase (decrease) in cash and cash equivalents	23,295	63,645	128,008
Cash and cash equivalents, beginning of period	104,713	60,392
Cash and cash equivalents, end of period	128,008	124,037	128,008
Supplementary disclosure of cash flow information:
Cash paid for interest
Cash paid for income taxes
Supplementary disclosure of noncash investing and financing activities:
Warrants issued to placement agents and investors			47,276
Exercise of liability-classified warrants to common shares	42	209	394
Convertible Preferred Stock
Supplementary disclosure of noncash investing and financing activities:
Preferred stock conversion/exercise of equity-classified warrants to common stock			16,760
Warrant
Supplementary disclosure of noncash investing and financing activities:
Preferred stock conversion/exercise of equity-classified warrants to common stock	$ 99	$ 132	$ 9,423