Unaudited Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATIONS:
Net income	$ 17,210		$ 19,123		$ 55,994	$ 55,106
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	62,994		61,099		126,083	121,807
Amortization of redemption premiums and expense on debt					1,977	2,087
Deferred income taxes and investment tax credit adjustments - net					5,866	860
Allowance for equity funds used during construction					(2,705)	(2,017)
Gain (Loss) on Extinguishment of Debt	0		2,415		0	2,415	$ 2,400
Change in certain assets and liabilities:
Accounts receivable					6,231	(2,589)
Inventories					9,900	(23,346)
Increase (Decrease) in Accounts Payable					22,316	(16,396)
Increase (Decrease) in Accrued Liabilities and Other Operating Liabilities					(3,934)	(3,996)
Accrued real estate and personal property taxes					3,553	21,144
Accrued interest					52	(1,951)
Pension and other postretirement benefit assets and liabilities					(8,284)	(3,452)
Short-term and long-term regulatory assets and liabilities					(21,026)	(799)
Increase (Decrease) in Prepaid Expense and Other Assets					12,526	3,169
Other - net					(4,398)	619
Net cash provided by operating activities					179,099	146,323
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures					(132,305)	(92,848)
Project development costs					(624)	(1,206)
Cost of removal and regulatory recoverable ARO payments					(12,562)	(19,488)
Other					0	101
Net cash used in investing activities					(145,491)	(113,441)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payments for financed capital expenditures					36	(0)
Proceeds from Issuance of Long-term Debt					0	474,568
Repayments of Lines of Credit					(75,000)	0
Distributions to Shareholders					62,579	53,227
Repayments of Long-term Debt					0	472,135
Payments of Deferred Finance Costs					(280)	(5,664)
Proceeds from Lines of Credit					100,000	30,000
Repayments of Long-term Debt					0	(472,135)
Preferred dividends of subsidiary	(804)	$ (803)	(804)	$ (803)	(1,607)	(1,607)
Other					(94)	(118)
Net cash used in financing activities					(39,596)	(28,183)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect					(5,988)	4,699
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	20,634		53,251		20,634	53,251	26,622	$ 48,552
Supplemental disclosures of cash flow information:
Capital Expenditures Incurred but Not yet Paid					56,465	35,617
Cash paid during the period for:
Income Taxes Paid, Net					5,000	12,000
Interest (net of amount capitalized)					59,195	62,167
Net income	17,210		19,123		55,994	55,106
Depreciation and amortization	62,994		61,099		126,083	121,807
Amortization of redemption premiums and expense on debt					1,977	2,087
Deferred income taxes and investment tax credit adjustments - net					5,866	860
Increase (Decrease) in Allowance for Equity Funds Used During Construction					2,705	2,017
Gain (Loss) on Extinguishment of Debt	$ 0		$ (2,415)		0	(2,415)	$ (2,400)
Increase (Decrease) in Regulatory Assets and Liabilities					21,026	799
Increase (Decrease) in Prepaid Expense and Other Assets					12,526	3,169
Other - net					(4,398)	619
Net Cash Provided by (Used in) Operating Activities					179,099	146,323
Increase (Decrease) in Accounts Receivable					(6,231)	2,589
Increase (Decrease) in Inventories					(9,900)	23,346
Increase (Decrease) in Accounts Payable					22,316	(16,396)
Increase (Decrease) in Accrued Liabilities and Other Operating Liabilities					(3,934)	(3,996)
Increase (Decrease) in Property and Other Taxes Payable					3,553	21,144
Accrued interest					52	(1,951)
Pension and other postretirement benefit assets and liabilities					$ (8,284)	$ (3,452)