Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities:
Net income	$ 196,763	$ 136,598	$ 115,932
Non-cash items included in net income:
Depreciation and amortization	205,994	187,318	175,655
Deferred income tax expense	15,098	8,570	69,657
Power and natural gas cost amortizations (deferrals), net	(45,917)	10,263	11,741
Amortization of debt expense	2,680	2,967	3,254
Amortization of investment in exchange power	1,633	2,450	2,450
Stock-based compensation expense	11,353	5,367	7,359
Equity-related AFUDC	(6,585)	(6,554)	(6,669)
Pension and other postretirement benefit expense	36,417	32,017	37,074
Other regulatory assets and liabilities and deferred debits and credits	65	27,512	(9,144)
Change in decoupling regulatory deferral	(10,327)	(1,288)	24,179
Gain (Loss) on Disposition of Business	(7,450)	0	0
Other	(13,526)	1,114	1,860
Contributions to defined benefit pension plan	(22,000)	(22,000)	(22,000)
Cash paid on settlement of interest rate swap agreements	(13,325)	(32,174)	(11,302)
Cash received on settlement of interest rate swap agreements	0	5,594	2,479
Changes in certain current assets and liabilities:
Accounts and notes receivable	(4,366)	15,474	(9,270)
Materials and supplies, fuel stock and stored natural gas	(6,148)	(5,807)	(4,767)
Collateral posted for derivative instruments	63,974	(4,128)	(22,394)
Income taxes receivable	(8,736)	2,021	53,414
Other current assets	(3,657)	(2,589)	(2,106)
Accounts payable	7,471	(470)	(8,162)
Other current liabilities	(1,199)	(370)	1,058
Net cash provided by operating activities	398,212	361,885	410,298
Investing Activities:
Utility property capital expenditures (excluding equity-related AFUDC)	(442,510)	(424,350)	(412,339)
Issuance of notes receivable at subsidiaries	(7,303)	(3,555)	(3,700)
Equity and property investments made by subsidiaries	(13,508)	(13,283)	(13,680)
Proceeds from sale of METALfx (net of cash sold)	16,407	0	0
Other	1,403	756	(4,384)
Net cash used in investing activities	(445,511)	(440,432)	(434,103)
Financing Activities:
Net increase (decrease) in short-term borrowings	(4,200)	84,603	(15,000)
Proceeds from issuance of long-term debt	180,000	374,621	90,000
Maturity of long-term debt and capital leases	(92,660)	(277,438)	(3,287)
Issuance of common stock, net of issuance costs	64,573	1,207	56,380
Cash dividends paid	(102,772)	(98,046)	(92,460)
Other	(2,402)	(7,916)	(4,163)
Net cash provided by financing activities	42,539	77,031	31,470
Net increase (decrease) in cash and cash equivalents	(4,760)	(1,516)	7,665
Cash and cash equivalents at beginning of year	14,656	16,172	8,507
Cash and cash equivalents at end of year	9,896	14,656	16,172
Cash paid (received) during the year:
Interest	99,060	97,437	95,499
Income taxes paid	26,764	17,801	5,579
Income tax refunds	(979)	(3,025)	(47,086)
Non-cash financing and investing activities:
Accounts payable for capital expenditures	$ 25,644	$ 31,868	$ 31,157