Pension Plan and Employee Benefits - Amounts Recognized in Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
PENSION BENEFITS
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss occurring during period	$ (26,925)	$ 30,126
Net actuarial loss amortized during period	20,739	16,292
Prior service credit amortized during period	0	(60)
Net actuarial loss	117,773	165,437
OTHER BENEFITS
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss occurring during period	(81)	4,221
Net actuarial loss amortized during period	1,523	1,389
Prior service credit amortized during period	0	0
Net actuarial loss	22,785	21,342
SERP BENEFITS
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss occurring during period	(1,932)	9,621
Net actuarial loss amortized during period	1,228	3,185
Prior service credit amortized during period	(215)	(215)
Net actuarial loss	31,526	34,825
Prior service credit	$ (1,514)	$ (1,728)