Unaudited Condensed Consolidated Statements Of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
UTILITY OPERATING REVENUES	$ 336,909	$ 327,745
Operation:
Fuel	70,735	66,497
Other operating expenses	64,127	57,234
Power purchased	49,021	52,448
Maintenance	30,027	30,521
Depreciation and amortization	52,544	53,235
Taxes other than income taxes	12,274	11,134
Income taxes - net	15,953	16,404
Total utility operating expenses	294,681	287,473
UTILITY OPERATING INCOME	42,228	40,272
OTHER INCOME AND (DEDUCTIONS):
Allowance for equity funds used during construction	6,425	6,781
Miscellaneous income and (deductions) - net	(344)	(1,076)
Income tax benefit applicable to nonoperating income	3,770	3,463
Total other income and (deductions) - net	9,851	9,168
INTEREST AND OTHER CHARGES:
Interest on long-term debt	29,121	26,101
Other interest	367	742
Allowance for borrowed funds used during construction	(5,482)	(5,834)
Amortization of redemption premiums and expense on debt	1,077	1,026
Total interest and other charges - net	25,083	22,035
NET INCOME	26,996	27,405
LESS: PREFERRED DIVIDENDS OF SUBSIDIARY	803	803
NET INCOME APPLICABLE TO COMMON STOCK	$ 26,193	$ 26,602