STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating activities
Net income	$ 106,369	$ 89,901	$ 78,067
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	115,917	109,207	106,207
Demand side management program amortization	1,811	1,811	2,034
Deferred income taxes	54,119	55,508	25,312
Amortization of investment tax credits	(327)	(275)	(341)
Allowance for equity funds used during construction	(7,272)	(5,342)	(4,188)
Provision for bad debts	2,915	3,655	3,990
Net derivative losses	269	268	268
Changes in operating assets and liabilities:
Accounts receivable	(3,429)	(23,518)	1,691
Accrued unbilled revenues	5,250	6,042	(4,399)
Inventories	4,238	(5,726)	(2,702)
Prepayments and other	(3,901)	(2,480)	10,920
Accounts payable	(13,730)	(1,527)	(17,015)
Net regulatory assets and liabilities	24,243	6,090	(20,082)
Other current liabilities	1,780	5,717	3,902
Pension and other employee benefit obligations	(13,706)	(7,576)	(4,213)
Change in other noncurrent assets	(1,541)	1,509	(2,868)
Change in other noncurrent liabilities	(1,912)	(4,299)	747
Net cash provided by operating activities	271,093	228,965	177,330
Investing activities
Utility capital/construction expenditures	(384,626)	(308,223)	(309,408)
Proceeds from the sale of assets	0	0	87,823
Allowance for equity funds used during construction	7,272	5,342	4,188
Investments in utility money pool arrangement	(217,000)	(40,300)	(204,200)
Receipts from utility money pool arrangement	217,000	40,300	281,200
Other, net	0	221	0
Net cash used in investing activities	(377,354)	(302,660)	(140,397)
Financing activities
Proceeds from (repayment of) short-term borrowings, net	9,000	(49,000)	49,000
Proceeds from issuance of long-term debt	108,678	193,137	0
Repayment of long-term debt	0	(101,800)	(25,000)
Borrowings under utility money pool arrangement	265,000	293,500	483,200
Repayments under utility money pool arrangement	(270,000)	(288,500)	(483,200)
Capital contributions from parent	60,024	89,631	583
Dividends paid to parent	(66,609)	(64,401)	(67,101)
Net cash provided by (used in) financing activities	106,093	72,567	(42,518)
Net change in cash and cash equivalents	(168)	(1,128)	(5,585)
Cash and cash equivalents at beginning of period	650	1,778	7,363
Cash and cash equivalents at end of period	482	650	1,778
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(61,268)	(57,122)	(57,969)
Cash paid for income taxes, net	(13,763)	(2,245)	(7,277)
Supplemental disclosure of non-cash investing transactions:
Property, plant and equipment additions in accounts payable	$ 38,751	$ 23,570	$ 9,539