ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Tables)

12 Months Ended

Dec. 31, 2025

Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]

Schedule of Accumulated Other Comprehensive Income (Loss)

The following table sets forth the balance in accumulated other comprehensive income (loss) for the periods indicated:

	Accumulated Other Comprehensive Income (Loss)
	(Thousands of dollars)
January 1, 2024	$	(1,182)
Pension plan obligation
Other comprehensive income (loss) before reclassification, net of tax of $(281)	961
Amounts reclassified from accumulated other comprehensive loss, net of tax of $—	(1)
Available-for-sale securities
Other comprehensive income (loss) before reclassification, net of tax of $(24)	94
Amounts reclassified from accumulated other comprehensive loss, net of tax of $(1)	2
Other comprehensive income (loss)	1,056
December 31, 2024	(126)
Pension plan obligation
Other comprehensive income (loss) before reclassification, net of tax of $27	(91)
Amounts reclassified from accumulated other comprehensive loss, net of tax of $—	(1)
Available-for-sale securities
Other comprehensive income (loss) before reclassification, net of tax of $(61)	230
Amounts reclassified from accumulated other comprehensive loss, net of tax of $2	(8)
Other comprehensive income (loss)	130
December 31, 2025	$	4

Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]

The following table sets forth the effect of reclassifications from accumulated other comprehensive income (loss) in our consolidated statements of income for the periods indicated:

							Affected Line Item in the
Details About Accumulated Other	Year Ended December 31,						Consolidated Statements
Comprehensive Income (Loss) Components	2025		2024		2023		of Income
	(Thousands of dollars)
Pension and other postemployment benefit plan obligations (a)
Amortization of net gain (loss)	$	(7,335)	$	(5,770)	$	(1,960)
Amortization of unrecognized prior service credit (cost)	(372)		(372)		(525)
	(7,707)		(6,142)		(2,485)
Regulatory adjustments (b)	7,708		6,143		2,486
Amounts reclassified from accumulated other comprehensive income (loss)	1		1		1		Other income (expense), net
Available-for-sale securities
Amounts reclassified from accumulated other comprehensive income (loss)	10		(3)		—		Other income (expense), net
Total reclassifications before tax	11		(2)		1		Income before income taxes
Tax effect of reclassifications	(2)		1		—		Income tax expense
Net reclassifications for the period	$	9	$	(1)	$	1	Net income

(a) These components of accumulated other comprehensive income (loss) are included in the computation of net periodic benefit cost (credit). See Note 11 for additional detail on our net periodic benefit cost (credit).

(b) Regulatory adjustments represent pension and other postemployment benefit credits or costs expected to be recovered through rates and are deferred as part of our regulatory assets. See Note 3 for additional disclosures of regulatory assets and liabilities.