Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Corporate and municipal bonds	$ 32.7	$ 29.0
Maturity dates of bonds, start date	2014-05
Maturity dates of bonds, end date	2019-11