Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended		115 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013
Cash flows from operating activities:
Net loss	$ (12,799)	$ (24,470)	$ (296,523)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	199	118	2,773
Stock-based compensation	1,541	1,212	21,722
Change in fair value of warrants	(10,788)	5,811	(21,559)
Loss on disposal of fixed assets			57
Common stock issued in exchange for in-process research and development			36,151
(Increase) decrease in:
Receivables	(14)	79	(72)
Prepaid expenses and other current assets	2,078	(9,490)	(4,834)
Other noncurrent assets	258	(23)	(743)
Deposits			(134)
Increase (decrease) in:
Accounts payable	(526)	257	983
Accrued expenses	2,005	713	18,521
Deferred revenue	(200)	(200)	3,333
Deferred rent	3	133	442
Net cash used in operating activities	(18,243)	(25,860)	(239,883)
Cash flows from investing activities:
Purchases of property and equipment	(114)	(154)	(4,740)
Proceeds from sale of property and equipment			1
Net cash used in investing activities	(114)	(154)	(4,739)
Cash flows from financing activities:
Stockholders' capital contribution			500
Proceeds from exercise of stock options	851		2,224
Payments to employees for repurchase of common stock	(246)		(3,113)
Proceeds from exercise of warrants	101	140	13,180
Proceeds from issuance of common stock and warrants, net		49,169	270,726
Proceeds from issuance of preferred stock, net			16,760
Net cash provided by financing activities	706	49,309	300,277
Net increase (decrease) in cash and cash equivalents	(17,651)	23,295	55,655
Cash and cash equivalents, beginning of period	73,306	104,713
Cash and cash equivalents, end of period	55,655	128,008	55,655
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	352
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	$ 72	$ 99	$ 9,396