Employee Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pension and SERPA Benefits:
Defined Benefit Plan Disclosure
Service cost	$ 1,175	$ 1,294
Interest cost	20,118	20,476
Expected return on plan assets	(33,143)	(36,519)
Amortization of unrecognized: Prior service cost (credit)	188	188
Amortization of unrecognized: Net (gain) loss	(163)	(181)
Settlement gain	0	(222)
Net periodic benefit income	(11,825)	(14,964)
Postretirement Healthcare Benefits:
Defined Benefit Plan Disclosure
Service cost	723	797
Interest cost	2,694	2,772
Expected return on plan assets	(4,424)	(4,281)
Amortization of unrecognized: Prior service cost (credit)	149	(166)
Amortization of unrecognized: Net (gain) loss	(1,250)	(1,097)
Net periodic benefit income	$ (2,108)	$ (1,975)