Pension Plan and Employee Benefits - Components of Periodic Benefit Costs and Weighted-Average Assumptions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
PENSION BENEFITS
Components of periodic benefit costs
Service cost	$ 10,516	$ 9,820	$ 8,414
Interest cost	18,668	20,816	22,485
Expected return on plan assets	(22,801)	(24,974)	(26,502)
Amortizations
Prior service credit	0	(60)	(71)
Net loss	20,738	16,292	7,849
Net periodic benefit cost	27,121	21,894	12,175
Special/contractual termination benefits	3,270	0	0
Total benefit cost	$ 30,391	$ 21,894	$ 12,175
Weighted-average assumptions used to determine the benefit obligation
Discount rate	2.98%	2.74%
Rate of compensation increase	2.73%	2.75%
Weighted-average assumptions used to determine the net benefit cost
Discount rate	2.74%	3.43%	4.35%
Expected return on plan assets	5.00%	5.91%	6.55%
Rate of compensation increase	2.71%	2.75%	2.81%
OTHER BENEFITS
Components of periodic benefit costs
Service cost	$ 2,425	$ 2,153	$ 1,191
Interest cost	1,283	1,651	1,646
Expected return on plan assets	0	0	0
Amortizations
Prior service credit	0	0	0
Net loss	1,523	1,389	21
Net periodic benefit cost	5,231	5,193	2,858
Special/contractual termination benefits	0	0	0
Total benefit cost	$ 5,231	$ 5,193	$ 2,858
Weighted-average assumptions used to determine the benefit obligation
Discount rate	2.82%	2.39%
Weighted-average assumptions used to determine the net benefit cost
Discount rate	2.39%	3.25%	4.16%
SERP BENEFITS
Components of periodic benefit costs
Service cost	$ 232	$ 399	$ 330
Interest cost	2,538	2,932	3,326
Amortizations
Prior service credit	(215)	(215)	(160)
Net loss	1,228	3,186	1,544
Total benefit cost	$ 3,783	$ 6,302	$ 5,040
Weighted-average assumptions used to determine the benefit obligation
Discount rate	2.95%	2.64%
Weighted-average assumptions used to determine the net benefit cost
Discount rate	2.64%	3.37%	4.34%
Rate of compensation increase			5.00%