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Interest rate stated in the contractual debt agreement.

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Significant Accounting Policies (Details 3) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
Significant Accounting Policies (Details 3) (USD $)	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Y D entity count	Sep. 30, 2010	Dec. 31, 2010 entity
Consolidation of variable interest entities
Number of variable interest entities in which the entity is not primary beneficiary			8		8
Comprehensive loss:
Unrealized holding gains (losses)	$ (1,552,000)	$ 221,000	$ (2,102,000)	$ (66,000)
Reclassification adjustment for realized loss included in net loss				(925,000)
Net loss	(26,882,000)	(12,454,000)	(64,765,000)	(47,265,000)
Comprehensive loss	(28,434,000)	(12,233,000)	(66,867,000)	(48,256,000)
Convertible debt
Interest rate on convertible debt (as a percent)	2.625%		2.625%
Regulus Therapeutics Inc.
Equity method of accounting
Principal plus accrued interest guaranteed on Regulus convertible notes	$ 5,400,000		$ 5,400,000