Pension Plan and Employee Benefits - Net Periodic Pension and Benefits Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
PENSION BENEFITS
Components of periodic benefit costs
Service cost	$ 2,146	$ 2,629	$ 6,439	$ 7,887
Interest cost	4,960	4,667	14,881	14,001
Expected return on plan assets	(6,177)	(5,700)	(18,531)	(17,101)
Amortizations
Net loss	3,084	5,184	9,251	15,553
Net periodic benefit cost	4,013	6,780	12,040	20,340
Special/contractual termination benefits	0	3,270	0	3,270
Total benefit cost	4,013	10,050	12,040	23,610
OTHER BENEFITS
Components of periodic benefit costs
Service cost	551	629	1,653	1,819
Interest cost	371	317	1,113	962
Expected return on plan assets	0	0	0	0
Amortizations
Net loss	303	373	908	1,143
Net periodic benefit cost	1,225	1,319	3,674	3,924
Special/contractual termination benefits	0	0	0	0
Total benefit cost	1,225	1,319	3,674	3,924
SERP
Components of periodic benefit costs
Service cost	57	59	170	174
Interest cost	670	634	2,009	1,903
Prior period service credit	(54)	(54)	(161)	(161)
Amortizations
Net loss	262	307	787	921
Total benefit cost	$ 935	$ 946	$ 2,805	$ 2,837