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Pension and Other Post-Retirement Benefits And Employee Benefits - Additional Information (Detail) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
 [1]
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     $ 6,900,000    
Amount recognized of net actuarial loss into net periodic benefit cost $ 1,732,000 [1] $ 1,831,000 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%    
Expected contribution to defined benefit plan for the fiscal year 0        
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 11,000 [1] 6,000 25,000 124,000 309,000
Amortization of past-service liability (62,000) [1] $ (62,000) $ (249,000) $ (249,000) $ (249,000)
Discount rates used to determine the benefit obligation     2.00% 2.90%  
Expected contribution to defined benefit plan for the fiscal year $ 915,000        
[1] Amounts are included in G&A expense on the Consolidated Statements of Income and Comprehensive Income.