Summary of Fair Value Accumulated Other Comprehensive Income and Intraperiod Tax Allocation in Available-for-Sale Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Investment in equity securities of Regulus, as reported	$ 55,478		$ 45,452
Intraperiod tax allocation recorded as an accrued liability	(6,825)
Accumulated other comprehensive income, net of tax	5,313	5,159
Regulus Therapeutics Inc
Schedule of Available-for-sale Securities [Line Items]
Carrying value	12,449	12,449	12,449	12,449
Accumulated other comprehensive income, before tax	43,029	35,217	33,003	26,299
Investment in equity securities of Regulus, as reported	55,478	47,666	45,452	38,748
Accumulated other comprehensive income, before tax	43,029	35,217	33,003	26,299
Intraperiod tax allocation recorded as a benefit from income taxes	(15,966)	(11,134)	(13,267)	(10,572)
Intraperiod tax allocation recorded as an accrued liability	(1,380)	(3,023)
Accumulated other comprehensive income, net of tax	25,683	21,060	19,736	15,727
Accumulated other comprehensive income, before tax	10,026	8,918
Investment in equity securities of Regulus, as reported	10,026	8,918
Accumulated other comprehensive income, before tax	10,026	8,918
Intraperiod tax allocation recorded as a benefit from income taxes	(2,699)	(562)
Intraperiod tax allocation recorded as an accrued liability	(1,380)	(3,023)
Accumulated other comprehensive income, net of tax	$ 5,947	$ 5,333