Regulus - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended					12 Months Ended		6 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2010	Sep. 30, 2012	Dec. 31, 2011	Mar. 31, 2009	Dec. 31, 2012 Regulus Therapeutics Inc	Mar. 31, 2009 Isis	Jun. 30, 2010 Sanofi	Dec. 31, 2010 Sanofi
Schedule Of Equity Method Investments Joint Ventures [Line Items]
Preferred stock purchased						$ 10,000,000		$ 10,000,000
Equity method investments									10,000,000
Gain loss on equity investment	16,084,000	16,084,000	4,421,000				16,100,000			4,421,000
Company ownership percentage				44.00%
Company ownership percentage	17.00%
Investment in equity securities of Regulus Therapeutics Inc	38,748,000	38,748,000					0
Increase in carrying value	12,400,000	12,400,000					12,400,000
Unrealized gain in other comprehensive income		15,700,000
Net of an intraperiod tax benefit	(10,572,000)	(10,572,000)
Prepaid expenses and other current assets	$ 2,540,000	$ 2,540,000			$ 4,158,000		$ 600,000