STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net income	$ 152,157	$ 127,263	$ 129,852
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	162,957	153,241	137,947
Demand side management program amortization	1,673	1,673	1,673
Deferred income taxes	122,983	62,836	123,517
Amortization of investment tax credits	(213)	(213)	(341)
Allowance for equity funds used during construction	(9,981)	(7,378)	(12,118)
Provision for bad debts	6,066	4,655	4,137
Net derivative losses	217	268	268
Other	122	(3,827)	0
Changes in operating assets and liabilities:
Accounts receivable	(8,868)	(3,291)	9,045
Accrued unbilled revenues	(15,637)	25,506	(20,080)
Inventories	(959)	5,686	(6,093)
Prepayments and other	22,651	(24,712)	(11,905)
Accounts payable	13,776	(24,570)	11,428
Net regulatory assets and liabilities	(55,689)	26,452	(973)
Other current liabilities	5,156	(30,762)	12,665
Pension and other employee benefit obligations	(15,276)	(9,405)	(2,246)
Change in other noncurrent assets	(200)	2,352	2,836
Change in other noncurrent liabilities	6,748	8,974	7,166
Net cash provided by operating activities	387,683	314,748	386,778
Investing activities
Utility capital/construction expenditures	(512,522)	(599,511)	(554,936)
Allowance for equity funds used during construction	9,981	7,378	12,118
Proceeds from insurance recoveries	3,901	0	0
Investments in utility money pool arrangement	(75,000)	(92,000)	(105,000)
Receipts from utility money pool arrangement	75,000	92,000	105,000
Other	(1,174)	3,136	0
Net cash used in investing activities	(499,814)	(588,997)	(542,818)
Financing activities
Proceeds from (repayment of) short-term borrowings, net	35,000	(22,000)	(47,000)
Proceeds from issuance of long-term debt	295,985	198,496	148,123
Repayment of long-term debt	(200,000)	0	0
Borrowings under utility money pool arrangement	636,500	579,700	458,000
Repayments under utility money pool arrangement	(636,500)	(595,700)	(480,000)
Capital contributions from parent	66,225	214,535	160,000
Dividends paid to parent	(85,069)	(100,544)	(83,498)
Net cash provided by financing activities	112,141	274,487	155,625
Net change in cash and cash equivalents	10	238	(415)
Cash and cash equivalents at beginning of period	834	596
Cash and cash equivalents at end of period	844	834	596
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(78,236)	(76,474)	(70,748)
Cash paid for income taxes, net	61,813	(23,987)	42,679
Supplemental disclosure of non-cash investing transactions:
Property, plant and equipment additions in accounts payable	$ 43,074	$ 44,335	$ 33,164