Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities:
Net income	$ 88,583	$ 90,846	$ 103,539
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of electric plant in service	79,626	78,556	81,331
Amortization of nuclear fuel	42,537	42,953	37,018
Deferred income taxes, net	44,678	43,561	45,688
Allowance for equity funds used during construction	(10,008)	(9,427)	(8,161)
Other amortization and accretion	16,556	14,724	19,875
Other operating activities	(925)	(479)	1,036
Change in:
Accounts receivable	(2,450)	13,448	(4,663)
Inventories	(3,673)	(1,926)	(3,750)
Net overcollection (undercollection) of fuel revenues	(10,843)	11,668	(26,001)
Prepayments and other	(4,295)	(2,784)	(2,538)
Accounts payable	8,180	1,725	4,401
Taxes accrued	(627)	(3,054)	11,915
Other current liabilities	958	78	(2,262)
Deferred charges and credits	(822)	(6,781)	(5,911)
Net cash provided by operating activities	247,475	273,108	251,517
Cash flows from investing activities:
Cash additions to utility property, plant and equipment	(237,411)	(202,387)	(178,041)
Cash additions to nuclear fuel	(30,535)	(46,009)	(39,551)
Capitalized interest and AFUDC:
Utility property, plant and equipment	(16,063)	(15,000)	(13,009)
Nuclear fuel	(5,299)	(5,312)	(5,177)
Allowance for equity funds used during construction	10,008	9,427	8,161
Decommissioning trust funds:
Purchases, including funding of $4.5 million, $4.5 million and $8.3 million, respectively	(65,491)	(107,705)	(95,441)
Sales and maturities	56,148	98,542	82,926
Proceeds from sale of investments in debt securities	0	0	2,000
Other investing activities	5,879	2,390	727
Net cash used for investing activities	(282,764)	(266,054)	(237,405)
Cash flows from financing activities:
Repurchases of common stock	0	0	(86,508)
Dividends paid	(42,049)	(38,889)	(27,223)
Borrowings under the revolving credit facility:
Proceeds	44,883	234,575	120,450
Payments	(52,686)	(245,799)	(91,775)
Pollution control bonds:
Proceeds	0	92,535	0
Payments	0	(92,535)	0
Proceeds from issuance of senior notes	0	149,682	0
Other financing activities	(324)	(3,774)	(32)
Net cash provided by (used for) financing activities	(50,176)	95,795	(85,088)
Net increase (decrease) in cash and cash equivalents	(85,465)	102,849	(70,976)
Cash and cash equivalents at beginning of period	111,057	8,208	79,184
Cash and cash equivalents at end of period	$ 25,592	$ 111,057	$ 8,208