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Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)
$ in Thousands
Jun. 30, 2015
Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Amount of fixed rate debt $ 383,147 $ 398,878
5.375% Fixed Rate Bonds [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Amount of fixed rate debt $ 250,000 $ 250,000
Interest rate on debt 5.375% 5.375%