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Financial Instruments (Bonds) - Additional Information (Detail) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2015
Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]    
Corporate and municipal bonds $ 39.9 $ 36.4
Maturity dates of bonds, start date 2015-10  
Maturity dates of bonds, end date 2020-10