Regulus - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended			12 Months Ended		1 Months Ended
	Mar. 31, 2009	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2013	Sep. 30, 2012	Dec. 31, 2013 Regulus Therapeutics Inc	Dec. 31, 2012 Regulus Therapeutics Inc	Mar. 31, 2009 Isis
Schedule Of Equity Method Investments Joint Ventures [Line Items]
Equity method investments	$ 10,000,000							$ 10,000,000
Company ownership percentage					44.00%
Company ownership percentage		17.00%
Investment in equity securities of Regulus Therapeutics Inc		38,700,000	38,700,000				0
Gain loss on equity investment		16,084,000	16,084,000				16,084,000
Increase in carrying value						12,449,000	12,449,000
Unrealized gain in other comprehensive income		15,727,000	15,727,000			19,736,000	15,727,000
Net of an intraperiod tax benefit		(10,572,000)	(10,572,000)			(2,695,000)
Prepaid expenses and other current assets		$ 2,641,000	$ 2,641,000	$ 3,910,000			$ 600,000