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Financial Instruments - Summary of Bond Activity (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Derivative Instruments And Hedging Activities Disclosure [Abstract]    
Fair value, Beginning Balance $ 29,776 $ 30,923
Purchases 5,650 5,742
Sales (845) (2,000)
Maturities and calls (4,050) (4,900)
Decrease in bond premium (270) (290)
Fair market value adjustment (250) 301
Fair value, Ending Balance $ 30,011 $ 29,776