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Financial Instruments - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
9 Months Ended
Sep. 30, 2014
Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]    
Corporate and municipal bonds $ 36.2 $ 29.0
Maturity dates of bonds, start date 2014-11  
Maturity dates of bonds, end date 2019-11