Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended		118 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013
Cash flows from operating activities:
Net loss	$ (31,491)	$ (48,083)	$ (315,215)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	396	265	2,970
Stock-based compensation	1,673	2,290	21,854
Change in fair value of warrants	(10,385)	6,461	(21,156)
Loss on disposal of fixed assets			57
Common stock issued in exchange for in-process research and development			36,151
(Increase) decrease in:
Receivables	27	79	(31)
Prepaid expenses and other current assets	2,845	(7,738)	(4,067)
Other noncurrent assets	269	(53)	(732)
Deposits	4	(41)	(130)
Increase (decrease) in:
Accounts payable	(344)	(258)	1,165
Accrued expenses	2,453	4,681	18,969
Deferred revenue	(400)	(400)	3,133
Deferred rent	(11)	172	428
Net cash used in operating activities	(34,964)	(42,625)	(256,604)
Cash flows from investing activities:
Purchases of property and equipment	(115)	(1,107)	(4,741)
Proceeds from sale of property and equipment			1
Net cash used in investing activities	(115)	(1,107)	(4,740)
Cash flows from financing activities:
Stockholders' capital contribution			500
Proceeds from exercise of stock options	854	30	2,227
Payments to employees for repurchase of common stock	(250)		(3,117)
Proceeds from exercise of warrants	101	210	13,180
Proceeds from issuance of common stock and warrants, net		49,170	270,726
Proceeds from issuance of preferred stock, net			16,760
Net cash provided by financing activities	705	49,410	300,276
Net increase (decrease) in cash and cash equivalents	(34,374)	5,678	38,932
Cash and cash equivalents, beginning of period	73,306	104,713
Cash and cash equivalents, end of period	38,932	110,391	38,932
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	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	$ 166	$ 9,396