Employee Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits
Net periodic benefit cost
Service cost	$ 3,817	$ 4,481	$ 12,082
Interest cost	10,106	7,730	6,911
Expected return on plan assets	(15,025)	(18,891)	(16,807)
Amortization of prior service cost	(3,280)	(3,280)	(3,237)
Effect of partial curtailment	(2,666)
Amortization of net loss	207	777	3,995
Net periodic benefit cost	(6,841)	(9,183)	2,944
Post-retirement Benefits
Net periodic benefit cost
Service cost	0	0	148
Interest cost	0	2	72
Expected return on plan assets	0	0	0
Amortization of prior service cost	0	(15,085)	(14,490)
Effect of partial curtailment	0	(26)	(20,177)
Amortization of net loss	0	2,824	2,607
Net periodic benefit cost	$ 0	$ (12,285)	$ (31,840)