CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenue:
Research and development revenue under collaborative agreements	$ 99,100	$ 96,190	$ 102,921
Licensing and royalty revenue	2,949	2,896	5,552
Total revenue	102,049	99,086	108,473
Expenses:
Research and development	158,458	157,397	145,160
General and administrative	12,515	12,789	11,669
Total operating expenses	170,973	170,186	156,829
Loss from operations	(68,924)	(71,100)	(48,356)
Other income (expense):
Equity in net loss of Regulus Therapeutics Inc.	(1,406)	(3,554)	(6,879)
Investment income	1,844	2,414	3,370
Interest expense	(21,152)	(16,732)	(13,232)
Gain (loss) on investments, net	1,465	4,182	(713)
Gain on investment in Regulus Therapeutics Inc.	18,356		4,651
Loss on early retirement of debt	(4,770)
Loss before income tax benefit (expense)	(74,587)	(84,790)	(61,159)
Income tax benefit (expense)	9,109	(11)	(92)
Net loss	$ (65,478)	$ (84,801)	$ (61,251)
Basic and diluted net loss per share (in dollars per share)	$ (0.65)	$ (0.85)	$ (0.62)
Shares used in computing basic net loss per share (in shares)	100,576	99,656	99,143
Shares used in computing diluted net loss per share (in shares)	100,576	99,656	99,143