Postretirement Benefits - Analysis of Impact on Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Impact on Other Comprehensive Income
Balance at January 1	$ (208,770)	$ (182,233)	$ (150,071)
Prior service cost (credit)	631	632	631
Net actuarial (gain) loss	20,166	16,000	7,843
Total amortization	20,797	16,632	8,474
Plan amendments	(4,565)	0	0
Experience gain (loss)(2)	61,299	(43,169)	(40,636)
Balance at December 31	(131,239)	(208,770)	(182,233)
Other Benefits
Defined Benefit Plan, Impact on Other Comprehensive Income
Total amortization	$ 228	$ 302	$ 265