Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
OPERATING ACTIVITIES:
Net income	$ 136,774	$ 135,508	$ 151,086
Adjustments to reconcile net cash provided (used) by operating activities:
Depreciation and amortization	114,384	113,180	112,004
Regulatory charges resulting from tax rate changes	19,621	23,580	23,580
Amortization of deferred charges and credits	(4,955)	(4,414)	(3,526)
Allowance for equity funds used during construction (equity AFUDC)	(2,335)	(1,360)	(414)
Changes in current assets and liabilities:
Trade and other accounts receivable	(515)	(1,632)	3,606
Affiliate receivables	(1,457)	(321)	58
Materials and supplies	(16)	898	(124)
Regulatory assets	(445)	111	(382)
Other current assets	(345)	(221)	719
Trade accounts payable	(1,230)	(3,571)	5,140
Affiliate payables	(1,025)	9,030	(5,062)
Regulatory liabilities	145,242	2	(19)
Other accrued liabilities	1,361	(877)	(8,584)
Regulatory liabilities	(140,190)	4,374	4,185
Other, net	3,773	(1,325)	1,651
Net cash provided (used) by operating activities	268,642	272,962	283,918
FINANCING ACTIVITIES:
Cash distributions to parent	(137,900)	(166,500)	(164,000)
Net cash provided (used) by financing activities	(137,900)	(166,500)	(164,000)
Property, plant and equipment:
Capital expenditures	(106,729)	(78,787)	(78,497)
Contributions and advances for construction costs	(10,555)	(10,268)	(6,103)
Disposal of property, plant and equipment, net	(5,369)	(4,370)	(920)
Advances to affiliate, net	(29,199)	(33,573)	(46,604)
Net cash provided (used) in investing activities	(130,742)	(106,462)	(119,918)
Increase (decrease) in cash	0	0	0
Cash at beginning of period	0	0	0
Cash at end of period	0	0	0
Supplemental Cash Flow Elements [Abstract]
Increases to property, plant and equipment, exclusive of equity AFUDC	(109,359)	(88,791)	(78,602)
Changes in related accounts payable and accrued liabilities	2,630	10,004	105
Capital expenditures	$ (106,729)	$ (78,787)	$ (78,497)