Employee Benefit Plans - Components of expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	$ 15,348	$ 12,644	$ 14,737
Defined benefit plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost	23,579	17,332	16,465
Expected return on plan assets, net of expenses	(25,221)	(24,900)	(23,235)
Amortization of actuarial loss and prior service cost	18	4,034	6,210
Total for defined benefit plans	(1,624)	(3,534)	(560)
SERPs
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost	708	509
Net periodic benefit cost	974	921	903
Defined contribution plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	$ 15,998	$ 15,257	$ 14,394