CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Activities:
Net income	$ 147,334	$ 129,488	$ 196,763
Non-cash items included in net income:
Depreciation and amortization	232,176	224,223	205,994
Provision for deferred income taxes	11,224	44,964	15,098
Power and natural gas cost amortizations (deferrals), net	(51,847)	(9,923)	(45,917)
Amortization of debt expense	2,606	3,237	2,680
Amortization of investment in exchange power			1,633
Stock-based compensation expense	4,713	5,846	11,353
Equity-related AFUDC	(7,004)	(6,970)	(6,585)
Pension and other postretirement benefit expense	29,077	33,812	36,417
Other regulatory assets and liabilities and deferred debits and credits	676	10,287	65
Change in decoupling regulatory deferral	6,056	2,971	(10,327)
Realized and unrealized gain on assets and investments	(23,187)	(5,170)	(13,077)
Other	(2,859)	2,373	(7,899)
Contributions to defined benefit pension plan	(42,000)	(22,000)	(22,000)
Cash paid on settlement of interest rate swap agreements	(17,568)	(33,499)	(13,325)
Cash received on settlement of interest rate swap agreements	324
Changes in certain current assets and liabilities:
Accounts and notes receivable	(46,107)	(10,960)	(4,366)
Materials and supplies, fuel stock and stored natural gas	(17,282)	(868)	(6,148)
Collateral posted for derivative instruments	(17,564)	1,579	63,974
Income taxes receivable	20,199	(41,363)	(8,736)
Other current assets	930	(2,401)	(3,657)
Accounts payable	33,369	(10,152)	7,471
Other current liabilities	4,074	15,530	(1,199)
Net cash provided by operating activities	267,340	331,004	398,212
Investing Activities:
Utility property capital expenditures (excluding equity-related AFUDC)	(439,939)	(404,306)	(442,510)
Issuance of notes receivable	(1,841)	(4,393)	(7,303)
Equity and property investments	(16,001)	(5,925)	(13,508)
Proceeds from sale of investments	8,306	6,786	16,407
Other	(4,559)	(2,905)	1,403
Net cash used in investing activities	(444,916)	(410,743)	(445,511)
Financing Activities:
Net increase (decrease) in short-term borrowings	81,000	17,200	(4,200)
Proceeds from issuance of long-term debt	140,000	165,000	180,000
Maturity of long-term debt and finance leases	(2,935)	(54,800)	(92,660)
Issuance of common stock, net of issuance costs	89,998	72,200	64,573
Cash dividends paid	(118,211)	(110,254)	(102,772)
Other	(4,304)	(5,307)	(2,402)
Net cash provided by financing activities	185,548	84,039	42,539
Net increase (decrease) in cash and cash equivalents	7,972	4,300	(4,760)
Cash and cash equivalents at beginning of year	14,196	9,896	14,656
Cash and cash equivalents at end of year	22,168	14,196	9,896
Cash paid (received) during the year:
Interest	98,592	97,717	99,060
Income taxes paid	3,652	1,901	26,764
Income tax refunds	(22,330)	(918)	(979)
Non-cash financing and investing activities:
Accounts payable for capital expenditures	$ 23,938	$ 32,039	$ 25,644