BENEFIT PLANS: Schedule of Amounts Recognized in Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022		Dec. 31, 2021	Dec. 31, 2020
Reclassification adjustments for:
Unfunded pension liability adjustment, net of tax	$ (27,118)		$ (3,318)	$ 7,074
Pension Plan
Defined Benefit Plan Disclosure
Actuarial (loss) gain during the year	227,372		91,156	(107,399)
Plan amendment service cost	0		0	0
Reclassification adjustments for:
Amortization of net loss	12,273		23,796	17,325
Amortization of prior service cost	6		6	6
Adjustment for deferred tax effects	(61,686)		(29,590)	23,184
Adjustment due to the effects of regulation	(177,965)		(85,368)	66,884
Unfunded pension liability adjustment, net of tax	0		0	0
Senior Management Security Plan
Defined Benefit Plan Disclosure
Actuarial (loss) gain during the year	32,009		(33)	(13,420)
Plan amendment service cost	0		0	(130)
Reclassification adjustments for:
Amortization of net loss	4,229		4,205	3,734
Amortization of prior service cost	279		296	290
Adjustment for deferred tax effects	(9,399)		(1,150)	2,452
Adjustment due to the effects of regulation	0		0	0
Unfunded pension liability adjustment, net of tax	27,118		3,318	(7,074)
Postretirement Benefits
Defined Benefit Plan Disclosure
Actuarial (loss) gain during the year	12,908		9,718	(6,515)
Plan amendment service cost	(8,065)		0	0
Reclassification adjustments for:
Immediate Recognition of loss from temporary deviation	0	[1]	4,736	0
Amortization of prior service cost	295		47	47
Adjustment for deferred tax effects	(1,315)		(2,514)	1,665
Adjustment due to the effects of regulation	(3,792)		(11,987)	4,803
Unfunded pension liability adjustment, net of tax	$ 0		$ 0	$ 0

[1] In 2021, a loss associated with a temporary deviation from the cost-sharing provisions of the substantive plan was recognized in "Other (income) expense, net" on the consolidated statements of income of the companies.