Pension Plan and Employee Benefits - Net Periodic Pension and Benefits Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
PENSION BENEFITS
Components of periodic benefit costs
Service cost	$ 2,143	$ 2,730	$ 4,293	$ 5,258
Interest cost	4,960	4,719	9,920	9,334
Expected return on plan assets	(6,177)	(5,698)	(12,354)	(11,400)
Amortizations
Net loss	3,083	5,607	6,168	10,369
Total benefit cost	4,009	7,358	8,027	13,561
OTHER BENEFITS
Components of periodic benefit costs
Service cost	551	595	1,102	1,190
Interest cost	371	323	742	645
Expected return on plan assets	0	0	0	0
Amortizations
Net loss	303	384	605	770
Total benefit cost	1,225	1,302	2,449	2,605
SERP
Components of periodic benefit costs
Service cost	57	61	113	116
Interest cost	670	644	1,340	1,269
Prior period service credit	(54)	(55)	(107)	(107)
Amortizations
Net loss	262	(401)	524	613
Total benefit cost	$ 935	$ 249	$ 1,870	$ 1,891