STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities
Net income	$ 127,263	$ 129,852	$ 95,177
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	153,241	137,947	124,069
Demand side management program amortization	1,673	1,673	1,673
Deferred income taxes	62,836	123,517	36,475
Amortization of Investment Tax Credits	(213)	(341)	(341)
Allowance for equity funds used during construction	(7,378)	(12,118)	(10,186)
Provision for bad debts	4,655	4,137	3,437
Gain on sale of transmission assets	0	0	(13,661)
Net derivative losses	268	268	268
Other Operating Activities, Cash Flow Statement	(3,827)	0	0
Changes in operating assets and liabilities:
Accounts receivable	(3,291)	9,045	(36,184)
Accrued unbilled revenues	25,506	(20,080)	(10,315)
Inventories	5,686	(6,093)	(7,443)
Prepayments and other	(24,712)	(11,905)	4,456
Accounts payable	(24,570)	11,428	20,650
Net regulatory assets and liabilities	26,452	(973)	620
Other current liabilities	(30,762)	12,665	51,880
Pension and other employee benefit obligations	(9,405)	(2,246)	(17,968)
Change in other noncurrent assets	2,352	2,836	(2,281)
Change in other noncurrent liabilities	8,974	7,166	(2,689)
Net cash provided by operating activities	314,748	386,778	237,637
Investing activities
Utility capital/construction expenditures	(599,511)	(554,936)	(584,736)
Allowance for equity funds used during construction	7,378	12,118	10,186
Proceeds from sale of transmission assets	0	0	37,118
Investments in utility money pool arrangement	(92,000)	(105,000)	(12,000)
Receipts from utility money pool arrangement	92,000	105,000	12,000
Payments for (Proceeds from) Other Investing Activities	3,136	0	0
Net cash used in investing activities	(588,997)	(542,818)	(537,432)
Financing activities
(Repayment of) proceeds from short-term borrowings, net	(22,000)	(47,000)	75,000
Proceeds from issuance of long-term debt	198,496	148,123	94,626
Borrowings under utility money pool arrangement	579,700	458,000	767,000
Repayments under utility money pool arrangement	(595,700)	(480,000)	(729,000)
Capital contributions from parent	214,535	160,000	162,277
Dividends paid to parent	(100,544)	(83,498)	(69,579)
Net cash provided by financing activities	274,487	155,625	300,324
Net change in cash and cash equivalents	238	(415)	529
Cash and cash equivalents at beginning of period	596	1,011	482
Cash and cash equivalents at end of period	834	596	1,011
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(76,474)	(70,748)	(67,209)
Cash paid for income taxes, net	(23,987)	42,679	(16,721)
Supplemental disclosure of non-cash investing transactions:
Property, plant and equipment additions in accounts payable	$ 44,335	$ 33,164	$ 23,305