Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 114,218	$ 98,816
Accounts receivable	448	636
Prepaid expenses and other current assets	579	763
Total current assets	115,245	100,215
Property and equipment, net	6,488	6,786
Other assets	27	27
Restricted investment	310	310
Total assets	122,070	107,338
Current liabilities:
Accounts payable	1,461	3,860
Accrued liabilities	7,447	6,933
Current portion of deferred revenue	3,512	3,349
Total current liabilities	12,420	14,142
Deferred revenue, less current portion	50,634	53,581
Other liabilities		63
Total liabilities	63,054	67,786
Commitments and contingencies (Note 6)
Stockholders' equity:
Common stock	347	300
Additional paid-in capital	374,929	311,755
Deficit accumulated during the development stage	(316,260)	(272,503)
Total stockholders' equity	59,016	39,552
Total liabilities and stockholders' equity	$ 122,070	$ 107,338