Pension and Other Postretirement Benefits - Pension Benefits - Net Periodic Pension (Income)/Cost (Details) - Pension Plan - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Pension Benefits
Service cost	$ 1,541	$ 1,417	$ 3,082	$ 2,835
Interest cost	15,582	16,494	31,165	32,987
Expected return on plan assets	(18,109)	(19,122)	(36,218)	(38,245)
Amortization of actuarial loss	3,600	1,553	7,200	3,107
Amortization of prior service credit	(486)	(486)	(972)	(972)
Effect of settlement	(27)	0	(27)	0
Net periodic pension (income)/cost or postretirement benefit cost	2,101	(144)	4,230	(288)
Qualified Plans
Pension Benefits
Service cost	1,541	1,417	3,082	2,835
Interest cost	13,376	14,198	26,752	28,396
Expected return on plan assets	(18,109)	(19,122)	(36,218)	(38,245)
Amortization of actuarial loss	2,603	663	5,206	1,327
Amortization of prior service credit	(486)	(486)	(972)	(972)
Effect of settlement	0	0	0	0
Net periodic pension (income)/cost or postretirement benefit cost	(1,075)	(3,330)	(2,150)	(6,659)
Non- Qualified Plans
Pension Benefits
Service cost	0	0	0	0
Interest cost	2,206	2,296	4,413	4,591
Expected return on plan assets	0	0	0	0
Amortization of actuarial loss	997	890	1,994	1,780
Amortization of prior service credit	0	0	0	0
Effect of settlement	(27)	0	(27)	0
Net periodic pension (income)/cost or postretirement benefit cost	$ 3,176	$ 3,186	$ 6,380	$ 6,371