CONSOLIDATED 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	$ 70,642	$ 59,468	$ 49,951
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	80,875	78,048	70,372
Deferred income taxes	45,396	25,789	27,107
Amortization of investment tax credits	(527)	(664)	(626)
Allowance for equity funds used during construction	(7,060)	(4,259)	(2,104)
Provision for bad debts	4,431	3,988	3,329
Net derivative losses (gains)	10	(279)	127
Changes in operating assets and liabilities:
Accounts receivable	(5,558)	(12,702)	(15,953)
Accrued unbilled revenues	(1,933)	(2,496)	(470)
Inventories	(3,210)	(1,879)	6,018
Other current assets	(3,501)	(3,749)	(3,172)
Accounts payable	2,936	(1,811)	5,828
Net regulatory assets and liabilities	(34,697)	(2,062)	3,623
Other current liabilities	(911)	7,589	3,681
Pension and other employee benefit obligations	(6,134)	(8,759)	(10,857)
Change in other noncurrent assets	(113)	232	14
Change in other noncurrent liabilities	2,534	1,119	(595)
Net cash provided by operating activities	143,180	137,573	136,273
Investing activities
Utility capital/construction expenditures	(288,209)	(201,278)	(152,759)
Allowance for equity funds used during construction	7,060	4,259	2,104
Other, net	(166)	(421)	916
Net cash used in investing activities	(281,315)	(197,440)	(149,739)
Financing activities
Proceeds from (repayments of) short-term borrowings, net	10,000	29,000	(27,000)
Proceeds from notes payable to affiliates	30	0	50
Repayments Of Notes Payable To Affiliates	0	(80)	0
Proceeds from Issuance of Long-term Debt	98,534	0	97,916
Repayments of long-term debt	(107)	(160)	(97)
Capital contributions from parent	73,432	58,977	2,796
Dividends paid to parent	(43,818)	(30,980)	(57,311)
Net cash provided by financing activities	138,071	56,757	16,354
Net change in cash and cash equivalents	(64)	(3,110)	2,888
Cash and cash equivalents at beginning of period	1,349	4,459	1,571
Cash and cash equivalents at end of period	1,285	1,349	4,459
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(24,442)	(24,376)	(21,035)
Cash received (paid) for income taxes, net	3,474	(9,842)	(5,841)
Supplemental disclosure of non-cash investing transactions:
Property, plant and equipment additions in accounts payable	$ 35,267	$ 27,222	$ 10,618