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Deferred Compensation Plan - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]    
Deferred compensation plan approved date under meeting May 11, 2004  
Directors and Executive Officers [Member]    
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]    
Deferred compensation obligation to directors and executive officers, included in other liability $ 3.6 $ 3.5