Unaudited Condensed Consolidated Statements Of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
UTILITY OPERATING REVENUES	$ 323,289	$ 292,477	$ 651,034	$ 624,678
Operation:
Fuel	53,167	77,084	119,664	162,516
Other operating expenses	62,209	54,832	119,443	109,808
Power purchased	40,421	31,409	92,869	73,985
Maintenance	36,480	40,755	67,001	72,037
Depreciation and amortization	57,916	42,931	111,151	89,376
Taxes other than income taxes	11,404	10,559	22,538	23,492
Income taxes - net	17,429	8,781	33,833	26,982
Total utility operating expenses	279,026	266,351	566,499	558,196
UTILITY OPERATING INCOME	44,263	26,126	84,535	66,482
OTHER INCOME AND (DEDUCTIONS):
Allowance for equity funds used during construction	6,596	3,079	13,377	6,297
Gains (Losses) on Extinguishment of Debt	0	(19,323)	0	(19,323)
Miscellaneous income and (deductions) - net	(58)	(742)	(1,134)	(1,368)
Income tax benefit applicable to nonoperating income	2,800	12,557	6,263	18,581
Total other income and (deductions) - net	9,338	(4,429)	18,506	4,187
INTEREST AND OTHER CHARGES:
Interest on long-term debt	27,452	27,695	53,553	55,341
Other interest	621	499	1,363	948
Allowance for borrowed funds used during construction	(5,624)	(2,567)	(11,458)	(5,233)
Amortization of redemption premiums and expense on debt	1,080	1,335	2,106	2,669
Total interest and other charges - net	23,529	26,962	45,564	53,725
NET INCOME (LOSS)	30,072	(5,265)	57,477	16,944
LESS: PREFERRED DIVIDENDS OF SUBSIDIARY	804	804	1,607	1,607
NET INCOME (LOSS) APPLICABLE TO COMMON STOCK	$ 29,268	$ (6,069)	$ 55,870	$ 15,337