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Summary of Information on Plans' Assets, Projected Benefit Obligations (PBO), and Funded Status (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Pension Plans      
Defined Benefit Plan Disclosure [Line Items]      
Plan Assets at Beginning of Year $ 126,098 $ 152,006  
Actual Return on Plan Assets 16,822 (19,984)  
Employer Contributions 3,850 3,800 $ 4,100
Benefits Paid (8,877) (9,724)  
Plan Assets at End of Year 137,893 126,098 152,006
PBO at Beginning of Year 146,953 199,418  
Service Cost 2,091 3,165 3,472
Interest Cost 7,480 5,486 5,003
Benefits Paid (8,877) (9,724) (6,489)
Actuarial (Gain) or Loss 6,920 (51,392)  
PBO at End of Year 154,567 146,953 199,418
Funded Status: Assets vs PBO (16,674) (20,855)  
Other Postretirement Benefit Plans, Defined Benefit      
Defined Benefit Plan Disclosure [Line Items]      
Plan Assets at Beginning of Year 44,770 42,651  
Actual Return on Plan Assets 6,865 (6,810)  
Employer Contributions 2,790 12,153 8,903
Participant Contributions 234 279  
Benefits Paid (2,767) (3,503)  
Plan Assets at End of Year 51,892 44,770 42,651
PBO at Beginning of Year 56,510 112,087  
Service Cost 1,493 2,890 3,034
Interest Cost 2,899 3,194 2,740
Benefits Paid (2,767) (3,503) (2,905)
Actuarial (Gain) or Loss 8,322 (58,437)  
PBO at End of Year 66,691 56,510 112,087
Funded Status: Assets vs PBO (14,799) (11,740)  
Supplemental Employee Retirement Plans, Defined Benefit      
Defined Benefit Plan Disclosure [Line Items]      
Employer Contributions 665 637 637
Benefits Paid (665) (637)  
PBO at Beginning of Year 14,810 17,714  
Service Cost 250 273 354
Interest Cost 754 472 458
Benefits Paid (665) (637) (637)
Actuarial (Gain) or Loss (295) (3,012)  
PBO at End of Year 14,854 14,810 $ 17,714
Funded Status: Assets vs PBO $ (14,854) $ (14,810)