Pension Plan and Employee Benefits - Net Periodic Pension and Benefits Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
PENSION BENEFITS
Components of periodic benefit costs
Service cost	$ 1,173	$ 2,040	$ 2,347	$ 4,086
Interest cost	6,606	4,960	13,211	9,920
Expected return on plan assets	(7,386)	(6,177)	(14,772)	(12,354)
Amortizations
Net loss (gain)	0	3,083	0	6,168
Net periodic benefit cost	393	3,906	786	7,820
OTHER BENEFITS
Components of periodic benefit costs
Service cost	365	546	729	1,092
Interest cost	566	368	1,132	736
Expected return on plan assets	0	0	0	0
Amortizations
Net loss (gain)	(13)	298	(25)	596
Net periodic benefit cost	918	1,212	1,836	2,424
SERP Benefits
Components of periodic benefit costs
Service cost	35	57	71	113
Interest cost	901	670	1,802	1,340
Amortizations
Prior period service credit	(54)	(54)	(107)	(107)
Net loss (gain)	(15)	262	(32)	524
Net periodic benefit cost	$ 867	$ 935	$ 1,734	$ 1,870