Pension and Other Postretirement Benefits - Pension Benefits - Net Periodic Pension (Income)/Cost (Details) - Pension Plan - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pension Benefits
Service cost	$ 1,541	$ 1,417
Interest cost	15,583	16,494
Expected return on plan assets	(18,109)	(19,122)
Amortization of actuarial loss	3,600	1,553
Amortization of prior service credit	(486)	(486)
Net periodic pension (income)/cost or postretirement benefit cost	2,129	(144)
Qualified Plans
Pension Benefits
Service cost	1,541	1,417
Interest cost	13,376	14,198
Expected return on plan assets	(18,109)	(19,122)
Amortization of actuarial loss	2,603	663
Amortization of prior service credit	(486)	(486)
Net periodic pension (income)/cost or postretirement benefit cost	(1,075)	(3,330)
Non- Qualified Plans
Pension Benefits
Service cost	0	0
Interest cost	2,207	2,296
Expected return on plan assets	0	0
Amortization of actuarial loss	997	890
Amortization of prior service credit	0	0
Net periodic pension (income)/cost or postretirement benefit cost	$ 3,204	$ 3,186