STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities
Net income	$ 129,852	$ 95,177	$ 106,369
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	137,947	124,069	115,917
Demand side management program amortization	1,673	1,673	1,811
Deferred income taxes	123,517	36,475	54,119
Amortization of investment tax credits	(341)	(341)	(327)
Allowance for equity funds used during construction	(12,118)	(10,186)	(7,272)
Provision for bad debts	4,137	3,437	2,915
Gain on sale of transmission assets	0	(13,661)	0
Net derivative losses	268	268	269
Changes in operating assets and liabilities:
Accounts receivable	9,045	(36,184)	(3,429)
Accrued unbilled revenues	(20,080)	(10,315)	5,250
Inventories	(6,093)	(7,443)	4,238
Prepayments and other	(11,905)	4,456	(3,901)
Accounts payable	11,428	20,650	(13,730)
Net regulatory assets and liabilities	(973)	620	24,243
Other current liabilities	12,665	51,880	1,780
Pension and other employee benefit obligations	(2,246)	(17,968)	(13,706)
Change in other noncurrent assets	2,836	(2,281)	(1,541)
Change in other noncurrent liabilities	7,166	(2,689)	(1,912)
Net cash provided by operating activities	386,778	237,637	271,093
Investing activities
Utility capital/construction expenditures	(554,936)	(584,736)	(384,626)
Proceeds from sale of transmission assets	0	37,118	0
Allowance for equity funds used during construction	12,118	10,186	7,272
Investments in utility money pool arrangement	(105,000)	(12,000)	(217,000)
Receipts from utility money pool arrangement	105,000	12,000	217,000
Other, net	0	0	0
Net cash used in investing activities	(542,818)	(537,432)	(377,354)
Financing activities
(Repayment of) proceeds from short-term borrowings, net	(47,000)	75,000	9,000
Proceeds from issuance of long-term debt	148,123	94,626	108,678
Borrowings under utility money pool arrangement	458,000	767,000	265,000
Repayments under utility money pool arrangement	(480,000)	(729,000)	(270,000)
Capital contributions from parent	160,000	162,277	60,024
Dividends paid to parent	(83,498)	(69,579)	(66,609)
Net cash provided by financing activities	155,625	300,324	106,093
Net change in cash and cash equivalents	(415)	529	(168)
Cash and cash equivalents at beginning of period	1,011	482	650
Cash and cash equivalents at end of period	596	1,011	482
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(70,748)	(67,209)	(61,268)
Cash paid for income taxes, net	42,679	(16,721)	(13,763)
Supplemental disclosure of non-cash investing transactions:
Property, plant and equipment additions in accounts payable	$ 33,164	$ 23,305	$ 38,751