Consolidated 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	$ 55,681	$ 54,971	$ 47,396
Adjustments to reconcile net income to cash flows from operating activities:
Depreciation and amortization including regulatory items	71,160	79,751	71,076
Pension and other postretirement benefit costs, net of contributions	1,689	(20,379)	(3,683)
Deferred income taxes and unamortized investment tax credit, net	31,899	45,051	26,880
Allowance for equity funds used during construction	(1,147)	(294)	(4,538)
Stock compensation expense	2,285	2,147	3,478
Non-cash loss on derivatives	4,174	1,187	1,853
Other	(16)	381
Cash flows impacted by changes in:
Accounts receivable and accrued unbilled revenues	(688)	10,342	(11,211)
Fuel, materials and supplies	369	(16,682)	(1,585)
Prepaid expenses, other current assets and deferred charges	(9,238)	(23,163)	(19,606)
Accounts payable and accrued liabilities	(1,297)	(318)	(6,179)
Interest, taxes accrued and customer deposits	875	(980)	1,522
Other liabilities and other deferred credits	3,360	3,172	3,954
SWPA minimum flows payment			26,564
Accumulated provision - rate refunds		(578)
Net cash provided by operating activities	159,106	134,608	135,921
Investing activities:
Capital expenditures - regulated	(134,272)	(99,162)	(106,388)
Capital expenditures and other investments - non-regulated	(2,670)	(3,375)	(2,817)
Restricted cash	(1)	(2,586)	(1,771)
Total net cash used in investing activities	(136,943)	(105,123)	(110,976)
Financing activities:
Proceeds from first mortgage bonds, net	88,000		149,635
Long-term debt issuance costs	(1,074)		(1,758)
Proceeds from issuance of common stock, net of issuance costs	8,114	5,884	60,239
Repayment of first mortgage bonds	(88,029)		(50,000)
Redemption of trust preferred securities			(50,000)
Redemption of senior notes			(48,304)
Net short-term borrowings (repayments)	12,000	(12,000)	(26,500)
Dividends	(42,273)	(26,732)	(51,996)
Other	(934)	(1,754)	(1,356)
Net cash used in financing activities	(24,196)	(34,602)	(20,040)
Net increase (decrease) in cash and cash equivalents	(2,033)	(5,117)	4,905
Cash and cash equivalents, beginning of year	5,408	10,525	5,620
Cash and cash equivalents, end of year	3,375	5,408	10,525
Supplemental cash flow information:
Interest paid	38,802	41,088	43,044
Income taxes (refunded) paid, net of refund	(592)	(14,300)	11,264
Supplementary non-cash investing activities:
Change in accrued additions to property, plant and equipment not reported above	9,345	(1,387)	(3,846)
Capital lease obligations for purchase of new equipment		$ 29	$ 2,696