Summary of Information on Plans' Assets, Projected Benefit Obligations (PBO), and Funded Status (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Beginning of Year	$ 137,406	$ 125,755
Actual Return on Plan Assets	16,989	13,024
Employer Contributions	4,100	4,665	$ 6,916
Benefits Paid	(6,489)	(6,038)
Plan Assets at End of Year	152,006	137,406	125,755
PBO at Beginning of Year	206,092	182,135
Service Cost	3,472	3,322	3,104
Interest Cost	5,003	5,776	6,484
Plan Amendments	674	732
Benefits Paid	(6,489)	(6,038)	(6,877)
Actuarial (Gain) or Loss	(9,334)	20,165
PBO at End of Year	199,418	206,092	182,135
Funded Status: Assets vs PBO	(47,412)	(68,686)
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Beginning of Year	32,847	27,280
Actual Return on Plan Assets	3,586	3,739
Employer Contributions	8,903	4,156	4,000
Participant Contributions	220	240
Benefits Paid	(2,905)	(2,568)
Plan Assets at End of Year	42,651	32,847	27,280
PBO at Beginning of Year	106,831	95,657
Service Cost	3,034	2,698	2,304
Interest Cost	2,740	3,121	3,426
Benefits Paid	(2,905)	(2,568)	(1,758)
Actuarial (Gain) or Loss	2,167	7,683
PBO at End of Year	112,087	106,831	95,657
Funded Status: Assets vs PBO	(69,436)	(73,984)
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Employer Contributions	637	654	610
Benefits Paid	(637)	(654)
PBO at Beginning of Year	20,225	17,759
Service Cost	354	283	247
Interest Cost	458	549	567
Benefits Paid	(637)	(654)	(610)
Actuarial (Gain) or Loss	(2,686)	2,288
PBO at End of Year	17,714	20,225	$ 17,759
Funded Status: Assets vs PBO	$ (17,714)	$ (20,225)