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Employee Benefit Plans - Additional Information (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Nov. 30, 2013
Defined Benefit Plan Disclosure [Line Items]        
Common stock held in employer stock fund 428,785 457,765   499,075
Total Company expenses under the health plan $ 3,060 $ 2,880 $ 3,020  
Deferred Compensation Liability 458 451    
Deferred compensation Expense 60 60 60  
Individual Counterparty        
Defined Benefit Plan Disclosure [Line Items]        
Stop Loss Insurance Liability 125      
Aggregate        
Defined Benefit Plan Disclosure [Line Items]        
Stop Loss Insurance Liability $ 4,080      
Supplemental Executive Retirement Plan        
Defined Benefit Plan Disclosure [Line Items]        
Defined Contribution Plan Maximum Employee Contribution As Percentage Of Average Compensation 35.00%      
Defined Benefit Plan, Employee Contribution, Age 62 years      
Defined benefit plan, actuarial obligation $ 7,080 $ 6,630    
Defined benefit plan, actuarial obligation Loss $ (111)      
Defined benefit plan, actuarial discount rate assumption 4.62% 4.41%    
401 (k) Savings Plan        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan Employer Matching Contributions $ 1,530 $ 1,580 $ 1,610  
Directors Plan        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Employee Contribution, Age 70 years      
Defined benefit plan, actuarial obligation $ 1,310 $ 997    
Defined benefit plan, actuarial discount rate assumption 4.62% 4.41%    
Defined Contribution Plan Maximum Employee Contribution As Percentage Of Base Salary 100.00%