CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Revenue:
Research and development revenue under collaborative agreements	$ 37,615	$ 47,140	$ 79,535	$ 68,957
Licensing and royalty revenue	477	200	1,916	1,618
Total revenue	38,092	47,340	81,451	70,575
Expenses:
Research and development	42,631	40,435	80,944	79,149
General and administrative	3,389	3,209	6,811	6,185
Total operating expenses	46,020	43,644	87,755	85,334
Income (loss) from operations	(7,928)	3,696	(6,304)	(14,759)
Other income (expense):
Equity in net loss of Regulus Therapeutics Inc.		(163)		(1,139)
Investment income	589	477	967	1,077
Interest expense	(4,808)	(5,219)	(9,603)	(10,398)
Gain on investments, net	840	2	1,898	19
Loss before income tax benefit (expense)	(11,307)	(1,207)	(13,042)	(25,200)
Income tax benefit (expense)	1,181		1,244	(2)
Net loss	$ (10,126)	$ (1,207)	$ (11,798)	$ (25,202)
Basic and diluted net loss per share (in dollars per share)	$ (0.09)	$ (0.01)	$ (0.11)	$ (0.25)
Shares used in computing basic net loss per share (in shares)	108,539	100,213	105,225	100,185
Shares used in computing diluted net loss per share (in shares)	108,539	100,213	105,225	100,185