Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended		106 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012
Cash flows from operating activities:
Net loss	$ (48,083)	$ (49,732)	$ (235,675)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	265	95	2,181
Stock-based compensation	2,290	1,314	17,591
Change in fair value of warrants	6,461	8,965	1,740
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
Prepaid expenses and other current assets	(7,738)	(592)	(9,051)
Other noncurrent assets	(53)	(519)	(824)
Deposits	(41)	(4)	(132)
Increase (decrease) in:
Accounts payable	(258)	753	1,469
Accrued expenses	4,681	3,546	15,502
Deferred revenue	(400)	4,733	3,933
Deferred rent	172	(5)	367
Net cash used in operating activities	(42,625)	(13,989)	(185,433)
Cash flows from investing activities:
Purchases of property and equipment	(1,107)	(392)	(4,174)
Proceeds from sale of property and equipment			1
Net cash used in investing activities	(1,107)	(392)	(4,173)
Cash flows from financing activities:
Stockholders' capital contribution			500
Proceeds from exercise of stock options	30	849	1,373
Payments to employees for repurchase of common stock		(78)	(2,321)
Proceeds from exercise of warrants	210	12,293	12,959
Proceeds from issuance of common stock and warrants, net	49,170	71,207	270,726
Proceeds from issuance of preferred stock, net			16,760
Net cash provided by financing activities	49,410	84,271	299,997
Net increase (decrease) in cash and cash equivalents	5,678	69,890	110,391
Cash and cash equivalents, beginning of period	104,713	60,392
Cash and cash equivalents, end of period	110,391	130,282	110,391
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	412	265	764
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 Exercise
Supplementary disclosure of noncash investing and financing activities:
Preferred stock conversion/exercise of equity-classified warrants to common stock	$ 166	$ 8,992	$ 9,490