Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended		111 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012
Cash flows from operating activities:
Net loss	$ (43,757)	$ (19,119)	$ (304,243)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	1,378	1,030	8,706
Accretion of investment discounts, net			(1,595)
Accretion of debt payment premium		64	999
Stock-based compensation	6,286	5,484	31,471
Loss on disposal of equipment and other non-cash items	177	11	2,461
Changes in operating assets and liabilities:
Accounts receivable	188	(240)	(448)
Prepaid expenses and other current assets	184	(31)	(804)
Other assets		3	113
Accounts payable	(1,879)	424	1,247
Accrued liabilities	233	(3,355)	7,086
Deferred revenue	(2,784)	57,767	54,146
Other liabilities	(55)	(33)	8
Net cash provided by (used in) operating activities	(40,029)	42,005	(200,853)
Cash flows from investing activities:
Purchase of intangible assets and in-process research and development			(412)
Purchase of property and equipment	(1,827)	(2,001)	(16,192)
Purchase of short-term investments			(169,497)
Sales and maturities of short-term investments			171,411
Purchase of restricted investment			(310)
Net cash used in investing activities	(1,827)	(2,001)	(15,000)
Cash flows from financing activities:
Proceeds from issuance of convertible notes payable			4,300
Proceeds from issuance of debt			31,006
Net proceeds from issuance of common stock through equity plans	1,128	1,786	7,839
Repayment of debt		(5,955)	(32,105)
Proceeds from issuance of common stock resulting from drawdown of equity line of credit, net of issuance costs			19,653
Proceeds from issuance of common stock in equity offerings, net of issuance costs	56,130	2	196,950
Proceeds from issuance of convertible preferred stock, net of issuance costs			102,428
Net cash provided by (used in) financing activities	57,258	(4,167)	330,071
Net increase in cash and cash equivalents	15,402	35,837	114,218
Cash and cash equivalents at beginning of period	98,816	76,007
Cash and cash equivalents at end of period	114,218	111,844	114,218
Supplemental disclosures of non-cash investing activities
Purchase of property and equipment through accounts payable	135	112	135
Deferred offering cost in accrued liability	273		273
Deferred offering cost in accounts payable	$ 50		$ 50