Postretirement Benefits - Analysis of Impact on Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan, Impact on Other Comprehensive Income
Balance at January 1	$ 1,570	$ (131,239)	$ (208,770)
Prior service cost (credit)	1,075	1,077	631
Net actuarial (gain) loss	(1,465)	12,677	20,166
Total amortization	(390)	13,754	20,797
Plan amendments	0	0	(4,565)
Experience gain (loss)	(3,907)	119,055	61,299
Balance at December 31	(2,727)	1,570	(131,239)
Other Benefits
Defined Benefit Plan, Impact on Other Comprehensive Income
Total amortization	$ (732)	$ 289	$ 228