XML 125 R110.htm IDEA: XBRL DOCUMENT v3.20.4
Employee Benefits - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]      
Percentage of company stock held equal to plan assets 12.00%    
Period of obligations for retired lives in trust 30 years    
Long term inflation rate 2.50%    
Company's contribution $ 5,700,000 $ 0  
Contribution to Health & Welfare Plan to pay premiums and claims in the next fiscal year $ 915,000    
Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Expected rate of return on equity security 6.00%    
Expected rate of return on fixed income security 3.00%    
Overall expected rate of return 5.00%    
Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Expected rate of return on equity security 8.00%    
Expected rate of return on fixed income security 5.00%    
Overall expected rate of return 7.00%    
Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Estimated unrecognized net actuarial loss (gain) that will be amortized from accumulated other comprehensive loss into net periodic benefit cost $ 6,900    
Amount recognized of net actuarial loss into net periodic benefit cost 7,327,000 $ 10,035,000 $ 7,179,000
Estimated prior service cost that will be amortized from accumulated other comprehensive loss (gain) into net periodic benefit cost 0    
Amortization of past-service liability $ 0    
Discount rates used to determine the benefit obligation 2.20% 3.00%  
Percentage of assets allocated to equities to be considered well funded 55.00%    
Percentage of assets allocated to fixed income to be considered well funded 44.00%    
Defined benefit plan cash equivalent portfolio percentage 1.00%    
Post-Retirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Estimated unrecognized net actuarial loss (gain) that will be amortized from accumulated other comprehensive loss into net periodic benefit cost $ 46,000 $ 249,000  
Amount recognized of net actuarial loss into net periodic benefit cost 25,000 124,000 309,000
Amortization of past-service liability $ (249,000) $ (249,000) $ (249,000)
Discount rates used to determine the benefit obligation 2.00% 2.90%