CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating Activities:
Net income	$ 155,176	$ 147,334	$ 129,488
Non-cash items included in net income:
Depreciation and amortization	253,142	232,176	224,223
Provision for deferred income taxes	(18,231)	11,224	44,964
Power and natural gas cost amortizations (deferrals), net	(78,350)	(51,847)	(9,923)
Amortization of debt expense	1,974	2,606	3,237
Stock-based compensation expense	8,717	4,713	5,846
Equity-related AFUDC	(6,704)	(7,004)	(6,970)
Pension and other postretirement benefit expense	32,173	29,077	33,812
Other regulatory assets and liabilities and deferred debits and credits	(20,409)	676	10,287
Change in decoupling regulatory deferral	33,469	6,056	2,971
Realized and unrealized gains on assets and investments	(50,006)	(23,187)	(5,170)
Other	11,957	(2,859)	2,373
Contributions to defined benefit pension plan	(42,000)	(42,000)	(22,000)
Cash paid on settlement of interest rate swap agreements	(17,035)	(17,568)	(33,499)
Cash received on settlement of interest rate swap agreements		324
Changes in certain current assets and liabilities:
Accounts and notes receivable	(56,007)	(46,107)	(10,960)
Materials and supplies, fuel stock and stored natural gas	(22,941)	(17,282)	(868)
Collateral posted for derivative instruments	(141,014)	(17,564)	1,579
Income taxes receivable	(1,125)	20,199	(41,363)
Other current assets	(6,613)	930	(2,401)
Accounts payable	65,928	33,369	(10,152)
Other current liabilities	22,106	4,074	15,530
Net cash provided by operating activities	124,207	267,340	331,004
Investing Activities:
Utility property capital expenditures (excluding equity-related AFUDC)	(451,995)	(439,939)	(404,306)
Issuance of notes receivable	(2,745)	(1,841)	(4,393)
Equity and property investments	(10,642)	(16,001)	(5,925)
Proceeds from sale of investments	1,000	8,306	6,786
Other	4,144	4,559	(2,905)
Net cash used in investing activities	(460,238)	(444,916)	(410,743)
Financing Activities:
Net increase (decrease) in short-term borrowings	179,000	81,000	17,200
Proceeds from issuance of long-term debt	399,856	140,000	165,000
Maturity of long-term debt and finance leases	(253,085)	(2,935)	(54,800)
Issuance of common stock, net of issuance costs	137,778	89,998	72,200
Cash dividends paid	(129,061)	(118,211)	(110,254)
Other	(7,197)	(4,304)	(5,307)
Net cash provided by financing activities	327,291	185,548	84,039
Net increase (decrease) in cash and cash equivalents	(8,740)	7,972	4,300
Cash and cash equivalents at beginning of year	22,168	14,196	9,896
Cash and cash equivalents at end of year	13,428	22,168	14,196
Cash paid (received) during the year:
Interest	107,468	98,592	97,717
Income taxes paid	2,251	3,652	1,901
Income tax refunds	(86)	(22,330)	(918)
Non-cash financing and investing activities:
Accounts payable for capital expenditures	$ 27,708	$ 23,938	$ 32,039