CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Revenue:
Research and development revenue under collaborative agreements	$ 11,127	$ 20,189	$ 80,085	$ 64,508
Licensing and royalty revenue	474	524	2,091	2,175
Total revenue	11,601	20,713	82,176	66,683
Expenses:
Research and development	36,551	39,924	115,700	110,178
General and administrative	3,096	3,105	9,281	8,989
Total operating expenses	39,647	43,029	124,981	119,167
Loss from operations	(28,046)	(22,316)	(42,805)	(52,484)
Other income (expense):
Equity in net loss of Regulus Therapeutics Inc.		(386)	(1,139)	(2,275)
Investment income	408	575	1,485	1,896
Interest expense	(5,937)	(4,773)	(16,335)	(11,624)
Gain (loss) on investments, net		18	19	(267)
Loss on early retirement of debt	(4,770)		(4,770)
Loss before income tax benefit (expense)	(38,345)	(26,882)	(63,545)	(64,754)
Income tax benefit (expense)	706		704	(11)
Net loss	$ (37,639)	$ (26,882)	$ (62,841)	$ (64,765)
Basic and diluted net loss per share (in dollars per share)	$ (0.37)	$ (0.27)	$ (0.63)	$ (0.65)
Shares used in computing basic net loss per share (in shares)	100,680	99,687	100,351	99,620
Shares used in computing diluted net loss per share (in shares)	100,680	99,687	100,351	99,620