Postretirement Benefits - Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Projected benefit obligation:
Projected benefit obligation, beginning of year	$ 1,246,159	$ 1,054,467
Service cost for benefits earned	53,041	43,492	$ 33,854
Interest cost on benefit obligation	36,824	37,578	39,306
Plan amendments	4,059	0
Actuarial (gain) loss	(38,400)	134,470
Benefits paid	(29,029)	(23,848)
Projected benefit obligation, end of year	1,272,654	1,246,159	$ 1,054,467
Accumulated benefit obligation, end of year	1,037,820	$ 1,006,884
Projected benefit obligations increase	$ 26,500
Discount rate used to measure future benefit obligations	3.16%	2.96%