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	$ 67,103	$ 63,445	$ 55,681
Adjustments to reconcile net income to cash flows from operating activities:
Depreciation and amortization including regulatory items	82,754	71,734	71,160
Pension and other postretirement benefit costs, net of contributions	1,973	(1,888)	1,689
Deferred income taxes and unamortized investment tax credit, net	41,693	28,272	31,899
Allowance for equity funds used during construction	(6,420)	(3,853)	(1,147)
Stock compensation expense	4,057	2,984	2,285
Loss on plant disallowance	86	2,409
Non-cash loss on derivatives	1,245	14	4,174
Regulatory reversal of gain on sale of assets	44	1,236
Other			(16)
Cash flows impacted by changes in:
Accounts receivable and accrued unbilled revenues	(24,174)	(14,312)	(688)
Fuel, materials and supplies	(8,121)	10,891	369
Prepaid expenses, other current assets and deferred charges	(6,051)	689	(9,238)
Accounts payable and accrued liabilities	1,141	(880)	(1,297)
Asset retirement obligation	(1,326)	(734)
Interest, taxes accrued and customer deposits	1,411	1,386	875
Other liabilities and other deferred credits	(4,192)	(3,942)	3,360
Net cash provided by operating activities	151,223	157,451	159,106
Investing activities:
Capital expenditures - regulated	(211,429)	(152,524)	(134,272)
Capital expenditures and other investments - non-regulated	(1,998)	(2,259)	(2,670)
Restricted cash	(1,854)	1,485	(1)
Total net cash used in investing activities	(215,281)	(153,298)	(136,943)
Financing activities:
Proceeds from first mortgage bonds, net	60,000	150,000	88,000
Long-term debt issuance costs	(651)	(1,879)	(1,074)
Proceeds from issuance of common stock, net of issuance costs	7,994	9,546	8,114
Repayment of first mortgage bonds			(88,029)
Redemption of senior notes		(98,000)
Net short-term borrowings/(repayments)	40,000	(20,000)	12,000
Dividends	(44,381)	(43,006)	(42,273)
Other	(274)	(714)	(934)
Net cash provided by / (used) in financing activities	62,688	(4,053)	(24,196)
Net increase (decrease) in cash and cash equivalents	(1,370)	100	(2,033)
Cash and cash equivalents, beginning of year	3,475	3,375	5,408
Cash and cash equivalents, end of year	2,105	3,475	3,375
Supplemental cash flow information:
Interest paid	40,127	39,033	38,802
Income taxes (refunded) paid, net of refund	23,103	10,584	(592)
Supplementary non-cash investing activities:
Change in accrued additions to property, plant and equipment not reported above	$ 9,427	$ 5,420	$ 9,345