Unaudited Condensed Consolidated Statements Of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
UTILITY OPERATING REVENUES	$ 326,562	$ 335,574	$ 951,240	$ 1,005,037
Operation:
Fuel	85,631	113,550	248,147	315,492
Other operating expenses	58,770	51,081	168,578	168,593
Power purchased	32,606	21,665	106,591	85,797
Maintenance	25,973	20,995	98,010	85,746
Depreciation and amortization	46,662	46,396	136,038	138,831
Taxes other than income taxes	10,061	11,191	33,553	34,403
Income taxes - net	21,404	21,385	48,386	49,147
Total utility operating expenses	281,107	286,263	839,303	878,009
UTILITY OPERATING INCOME	45,455	49,311	111,937	127,028
OTHER INCOME AND (DEDUCTIONS):
Allowance for equity funds used during construction	3,888	2,051	10,185	5,014
Loss on early extinguishment of debt	(2,728)	0	(22,051)	0
Miscellaneous income and (deductions) - net	(556)	(391)	(1,924)	(1,932)
Income tax benefit applicable to nonoperating income	5,521	5,545	24,102	16,696
Total other income and (deductions) - net	6,125	7,205	10,312	19,778
INTEREST AND OTHER CHARGES:
Interest on long-term debt	24,720	27,503	80,061	80,602
Other interest	539	467	1,487	1,386
Allowance for borrowed funds used during construction	(3,411)	(1,246)	(8,644)	(2,978)
Amortization of redemption premiums and expense on debt	1,086	1,321	3,755	3,956
Total interest and other charges - net	22,934	28,045	76,659	82,966
NET INCOME	28,646	28,471	45,590	63,840
LESS: PREFERRED DIVIDENDS OF SUBSIDIARY	803	803	2,410	2,410
NET INCOME APPLICABLE TO COMMON STOCK	$ 27,843	$ 27,668	$ 43,180	$ 61,430