Business Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Income Tax Expense (Benefit)	$ 4,505	$ 5,165	$ 14,540	$ 14,937
Net Income (Loss) Attributable to Parent	17,210	19,123	55,994	55,106
UTILITY OPERATING REVENUES	330,587	311,503	692,788	668,885
Depreciation and amortization	62,994	61,099	126,083	121,807
Interest Expense	32,199	33,935	62,266	64,016
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	21,715	24,288	70,534	70,043
Property, Plant and Equipment, Additions			132,341	92,848
Assets	4,994,205	4,969,919	4,994,205	4,969,919	$ 4,969,919
Interest Rate Cash Flow Hedge Liability at Fair Value	46,015		46,015
Electric [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	62,994	61,099	126,083	121,807
Interest Expense	21,255	21,882	42,776	43,802
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	32,587	38,770	89,882	93,737
Property, Plant and Equipment, Additions			132,341	92,848
Assets	4,975,344	4,952,408	4,975,344	4,952,408
Other Segments [Member]
Segment Reporting Information [Line Items]
UTILITY OPERATING REVENUES	0	0	0	0
Depreciation and amortization	0	0	0	0
Interest Expense	10,944	12,053	19,490	20,214
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	(10,872)	(14,482)	(19,348)	(23,694)
Property, Plant and Equipment, Additions			0	0
Assets	18,861	17,511	18,861	17,511
Electricity [Member]
Segment Reporting Information [Line Items]
UTILITY OPERATING REVENUES	$ 330,587	$ 311,503	$ 692,788	$ 668,885