Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands	6 Months Ended		114 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011
Operating activities
Net loss	$ (25,991)	$ (24,491)	$ (251,683)
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash interest expense			525
Depreciation and amortization	864	1,066	9,342
Amortization of non-cash compensation			522
Stock-based compensation - employees	5,302	3,219	32,361
Stock-based compensation - non-employees			853
Stock-based license payments			1,220
Change in fair value of warrant liability	1,354	(1,595)	3,218
Loss on disposal of asset			360
Impairment of leasehold improvements			1,030
Non-cash charge for in-process research and development			418
Debt instrument convertible beneficial conversion feature			135
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,817)	399	(5,053)
Other non-current assets			(288)
Accounts payable and accrued expenses	(1,271)	(3,883)	7,019
Deferred revenue	(1,354)		30,925
Net cash used in operating activities	(23,913)	(25,285)	(169,096)
Investing activities
Sale and redemption of marketable securities	57,224	52,525	630,838
Purchases of marketable securities	(36,594)	(38,125)	(688,229)
Purchases of property and equipment	(182)	(135)	(12,651)
Net cash provided by/(used in) investing activities	20,448	14,265	(70,042)
Financing activities
Proceeds from the issuance of preferred stock, net of issuance costs			143,022
Proceeds from the issuance of common stock and warrants, net of issuance costs		17,131	113,307
Proceeds from the issuance of convertible notes			5,000
Payments of capital lease obligations	(40)	(211)	(5,587)
Payments of secured loan agreement	(626)	(626)	(2,087)
Proceeds from exercise of stock options	348	9	1,639
Proceeds from exercise of warrants (common and preferred)			264
Proceeds from capital asset financing arrangement			5,611
Proceeds from secured loan agreement			3,758
Net cash provided by/(used in) financing activities	(318)	16,303	264,927
Net increase/(decrease) in cash and cash equivalents	(3,783)	5,283	25,789
Cash and cash equivalents at beginning of period	29,572	19,339
Cash and cash equivalents at end of period	25,789	24,622	25,789
Supplemental disclosures of cash flow information
Cash paid during the period for interest	89	157	1,973
Non-cash activities
Conversion of notes payable to preferred stock			5,000
Conversion of preferred stock to common stock			148,951
Accretion of redeemable convertible preferred stock			802
Beneficial conversion feature related to the issuance of Series C redeemable convertible preferred stock			$ 19,424