Annual report pursuant to Section 13 and 15(d)

Retirement Plans and Related Post Retirement Benefits - Narrative (Detail)

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Retirement Plans and Related Post Retirement Benefits - Narrative (Detail)
 12 Months Ended
Jan. 01, 2016
Dec. 31, 2017
USD ($)
retirement_plan
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Defined Benefit Plan Disclosure        
Number of non-qualified supplemental retirement defined benefit plans | retirement_plan   2    
Accumulated benefit obligation of the plans   $ 22,700,000 $ 18,600,000  
Fair value of plan assets at period end   0 0  
SERP        
Defined Benefit Plan Disclosure        
Unrecognized prior service costs   2,300,000    
Unrecognized prior service costs, net   3,500,000    
Unrecognized prior service costs, tax   1,200,000    
Unrecognized actuarial losses   6,000,000    
Unrecognized actuarial losses, net   8,600,000    
Unrecognized actuarial losses, tax   2,600,000    
Net periodic pension cost   300,000    
Net periodic pension cost net of tax   400,000    
Net periodic pension cost, tax   100,000    
Actuarial loss   400,000    
Actuarial loss, net of tax   600,000    
Actuarial loss, tax   200,000    
Current accrued pension liability   300,000    
Long-term accrued pension liability   24,800,000    
Expected future payments in 2018 (less than for SERP Medical)   300,000    
Expected future payments in 2019 (less than for SERP Medical)   300,000    
Expected future payments in 2020 (less than for SERP Medical)   300,000    
Expected future payments in 2021 (less than for SERP Medical)   300,000    
Expected future payments in 2022 (less than for SERP Medical)   300,000    
Benefits to be paid in the aggregate for the following five years   2,800,000    
SERP Medical        
Defined Benefit Plan Disclosure        
Unrecognized prior service costs   100,000    
Unrecognized actuarial losses   500,000    
Unrecognized actuarial losses, tax   200,000    
Current accrued pension liability   100,000    
Long-term accrued pension liability   1,200,000    
Expected future payments in 2018 (less than for SERP Medical)   100,000    
Expected future payments in 2019 (less than for SERP Medical)   100,000    
Expected future payments in 2020 (less than for SERP Medical)   100,000    
Expected future payments in 2021 (less than for SERP Medical)   100,000    
Expected future payments in 2022 (less than for SERP Medical)   100,000    
Benefits to be paid in the aggregate for the following five years   $ 300,000    
Annual increase in the cost of health care benefits   6.20%    
Change in retirement benefit obligation   $ 100,000    
Percentage of fund 91.20%      
Contributions of employer   $ 1,100,000 $ 1,100,000 $ 1,000,000
Total employer contribution   1.00%    
SERP Medical | Minimum        
Defined Benefit Plan Disclosure        
Annual increase in the cost of health care benefits range   4.20%    
SERP Medical | Maximum        
Defined Benefit Plan Disclosure        
Annual increase in the cost of health care benefits range   6.20%