Pension Plan and Employee Benefits - Components of Periodic Benefit Costs and Weighted-Average Assumptions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
PENSION BENEFITS
Components of periodic benefit costs
Service cost	$ 4,977	$ 8,589	$ 10,516
Interest cost	26,423	19,841	18,668
Expected return on plan assets	(29,544)	(24,706)	(22,801)
Amortizations
Net loss (gain)	0	12,332	20,738
Net periodic benefit cost	1,856	16,056	27,121
Special/contractual termination benefits	0	0	3,270
Total benefit cost	$ 1,856	$ 16,056	$ 30,391
Weighted-average assumptions used to determine the benefit obligation
Discount rate	5.13%	5.44%
Rate of compensation increase	3.50%	2.76%
Weighted-average assumptions used to determine the net benefit cost
Discount rate	5.44%	2.98%	2.74%
Expected return on plan assets	6.60%	5.25%	5.00%
Rate of compensation increase	2.76%	2.73%	2.71%
OTHER BENEFITS
Components of periodic benefit costs
Service cost	$ 1,472	$ 2,204	$ 2,425
Interest cost	2,285	1,484	1,283
Expected return on plan assets	0	0	0
Amortizations
Net loss (gain)	(45)	1,210	1,523
Net periodic benefit cost	3,712	4,898	5,231
Special/contractual termination benefits	0	0	0
Total benefit cost	$ 3,712	$ 4,898	$ 5,231
Weighted-average assumptions used to determine the benefit obligation
Discount rate	5.25%	5.61%
Weighted-average assumptions used to determine the net benefit cost
Discount rate	5.61%	2.82%	2.39%
SERP BENEFITS
Components of periodic benefit costs
Service cost	$ 142	$ 227	$ 232
Interest cost	3,604	2,679	2,538
Amortizations
Prior service credit	(215)	(215)	(215)
Net loss (gain)	(63)	1,049	1,228
Total benefit cost	$ 3,468	$ 3,740	$ 3,783
Weighted-average assumptions used to determine the benefit obligation
Discount rate	5.13%	5.46%
Weighted-average assumptions used to determine the net benefit cost
Discount rate	5.46%	2.95%	2.64%