Components of Retirement Plan Costs (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 523	$ 791
Interest Cost	1,870	1,371
Expected Return on Plan Assets	(2,672)	(2,720)
Prior Service Cost Amortization	89	89
Actuarial Loss Amortization		1,377
Sub-total	(190)	908
Amounts Capitalized and Deferred	498	(156)
Net Periodic Benefit Cost Recognized	308	752
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	373	722
Interest Cost	725	799
Expected Return on Plan Assets	(852)	(854)
Prior Service Cost Amortization	198	273
Actuarial Loss Amortization	(366)	255
Sub-total	78	1,195
Amounts Capitalized and Deferred	221	(511)
Net Periodic Benefit Cost Recognized	299	684
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	63	68
Interest Cost	188	118
Prior Service Cost Amortization	14	14
Actuarial Loss Amortization	0	199
Sub-total	265	399
Amounts Capitalized and Deferred	(82)	(118)
Net Periodic Benefit Cost Recognized	$ 183	$ 281