Pension Plan and Employee Benefits - Net Periodic Pension and Benefits Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
PENSION BENEFITS
Components of periodic benefit costs
Service cost	$ 1,173	$ 2,047
Interest cost	6,606	4,960
Expected return on plan assets	(7,386)	(6,177)
Amortizations
Net loss (gain)	0	3,085
Net periodic benefit cost	393	3,915
OTHER BENEFITS
Components of periodic benefit costs
Service cost	365	546
Interest cost	566	368
Expected return on plan assets	0	0
Amortizations
Net loss (gain)	(13)	298
Net periodic benefit cost	918	1,212
SERP Benefits
Components of periodic benefit costs
Service cost	35	57
Interest cost	901	670
Amortizations
Net loss (gain)	(15)	262
Prior period service credit	(54)	(54)
Net periodic benefit cost	$ 867	$ 935