Condensed Consolidated Balance Sheets (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Current assets:
Cash and cash equivalents	$ 68,820	$ 44,321
Available-for-sale securities	106,309	203,706
Accounts receivable	74	19
Related party accounts receivable, net	667	2,876
Prepaid expenses and other assets	2,896	5,320
Restricted cash		2,833
Total current assets	178,766	259,075
Restricted cash	7,647	7,647
Property and equipment, net	32,875	34,369
Other assets	192	274
Total assets	219,480	301,365
Current liabilities:
Accounts payable	2,390	4,302
Accrued research and development costs	7,629	8,140
Accrued expenses	9,247	8,938
Current portion of capital lease obligations	228	197
Current portion of deferred rent	3,707	2,799
Current portion of deferred revenue	47,647	40,050
Total current liabilities	70,848	64,426
Capital lease obligations, net of current portion	481	393
Deferred rent, net of current portion	13,308	14,612
Deferred revenue, net of current portion	21,913	62,383
Commitments and contingencies (Note 8)
Stockholders' equity:
Preferred stock, $0.001 par value, 75,000,000 shares authorized, no shares issued and outstanding
Additional paid-in capital	538,241	526,991
Accumulated deficit	(425,418)	(367,540)
Accumulated other comprehensive income	6	1
Total stockholders' equity	112,930	159,551
Total liabilities and stockholders' equity	219,480	301,365
Class A common stock
Stockholders' equity:
Common stock	59	48
Class B common stock
Stockholders' equity:
Common stock	$ 42	$ 51