Condensed Consolidated Statements Of Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Condensed Consolidated Statements Of Income [Abstract]
UTILITY OPERATING REVENUES	$ 314,160	$ 299,569	$ 669,463	$ 626,586
UTILITY OPERATING EXPENSES:
Fuel	97,844	94,092	201,942	199,799
Other operating expenses	55,393	58,778	117,512	113,549
Power purchased	26,384	18,073	64,132	41,284
Maintenance	32,778	29,092	64,751	54,107
Depreciation and amortization	46,380	45,455	92,435	90,505
Taxes other than income taxes	11,004	11,403	23,212	23,280
Income taxes - net	11,203	10,893	27,762	29,317
Total utility operating expenses	280,986	267,786	591,746	551,841
UTILITY OPERATING INCOME	33,174	31,783	77,717	74,745
OTHER INCOME AND (DEDUCTIONS):
Allowance for equity funds used during construction	1,350	889	2,963	1,611
Miscellaneous income and (deductions) - net	(566)	(648)	(1,541)	(1,185)
Income tax benefit applicable to nonoperating income	5,397	5,236	11,151	11,104
Total other income and (deductions) - net	6,181	5,477	12,573	11,530
INTEREST AND OTHER CHARGES:
Interest on long-term debt	26,659	26,463	53,099	52,513
Other interest	466	433	919	862
Allowance for borrowed funds used during construction	(749)	(511)	(1,732)	(921)
Amortization of redemption premiums and expense on debt	1,316	1,287	2,635	2,572
Total interest and other charges - net	27,692	27,672	54,921	55,026
NET INCOME	11,663	9,588	35,369	31,249
LESS: PREFERRED DIVIDENDS OF SUBSIDIARY	804	804	1,607	1,607
NET INCOME APPLICABLE TO COMMON STOCK	$ 10,859	$ 8,784	$ 33,762	$ 29,642