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Retirement Plans - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2017
USD ($)
Employee
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Defined Benefit Plan Disclosure [Line Items]      
Matching contribution to 401(k) plan $ 805,000 $ 734,000 $ 667,000
Employer matching contribution description The Company’s matching contribution is 100% of an employee’s first three percent contributed and 50% of the next two percent contributed.    
Pension plan eligibility age of employees 20 years 6 months    
Pension plan eligibility service period of employees 6 months    
Pension plan eligibility service hours of employees 1000 hours    
Additional benefits under pension plan $ 0    
Interest expense 4,092,000 3,308,000 3,309,000
Unrecognized actuarial loss 4,070,000 4,345,000  
Unrecognized actuarial net of tax 2,191,000 2,238,000  
Accumulated benefit obligation for defined benefit pension plan 17,916,000 16,964,000  
Net periodic benefit cost over the next fiscal year 380,000    
Incurred settlement cost $ 237,000 $ 259,000 $ 415,000
Rate of compensation increase used to determine the benefit obligation 0.00% 0.00% 0.00%
Long-term rate of return on plan assets 7.00% 7.00%  
Expected future employer contributions $ 0    
Employer contribution 2,000,000 $ 500,000  
Fund status 1,390,000 (814,000)  
Shortfall Agreements [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Pension shortfall expense 18,000 201,000 $ 364,000
Interest expense $ 18,000 11,000 10,000
Number of individuals under plan | Employee 10    
Supplemental Retirement Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Maximum retirement year for participants 10 years    
Liability recorded for supplemental retirement plan $ 2,308,000 1,984,000  
Expenses recorded for supplemental retirement plan 365,000 243,000 299,000
Total distribution to participant $ 41,000 $ 34,000 $ 22,000