CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
OPERATING ACTIVITIES:
Net Income	$ 186,840	$ 155,215	$ 202,120
Items not affecting cash:
Depreciation and depletion	187,467	179,644	172,923
Amortization of debt issuance costs, discount and deferred hedge gain	5,250	4,911	4,648
Stock-based compensation costs	5,350	4,149	8,007
Equity portion of allowance for funds used during construction	(11,092)	(6,895)	(5,768)
(Gain) loss on disposition of assets	(47)	37	(188)
Deferred income taxes	525	(7,574)	(13,864)
Changes in current assets and liabilities:
Accounts receivable	(30,442)	(824)	(5,032)
Inventories	(19,604)	(7,085)	(3,110)
Other current assets	(6,835)	(3,477)	(3,140)
Accounts payable	7,494	16,043	(1,821)
Accrued expenses	26,055	5,909	(16,023)
Regulatory assets	(69,616)	14,749	(16,028)
Regulatory liabilities	(27,674)	22,773	(7,796)
Other noncurrent assets	2,313	(5,396)	(22,841)
Other noncurrent liabilities	(36,006)	(20,030)	4,633
Cash Provided by Operating Activities	219,978	352,149	296,720
INVESTING ACTIVITIES:
Property, plant, and equipment additions	(434,328)	(405,762)	(316,016)
Investment in equity securities	(1,505)	(42)	(135)
Cash Used in Investing Activities	(435,833)	(405,804)	(316,151)
FINANCING ACTIVITIES:
Dividends on common stock	(128,483)	(120,350)	(115,127)
Proceeds from issuance of common stock, net	196,246	0	0
Issuance of long-term debt	99,915	150,000	150,000
Payment for Debt Extinguishment or Debt Prepayment Cost	(955)	0	0
Line of credit borrowings (repayments), net	151,000	(67,000)	(19,000)
(Repayments) issuances of short-term borrowings	(100,000)	100,000	0
Treasury stock activity	707	(1,391)	1,432
Financing costs	(909)	(2,578)	(1,115)
Cash Provided by Financing Activities	217,521	58,681	16,190
Net Increase (Decrease) in Cash, Cash Equivalents, and Restricted Cash	1,666	5,026	(3,241)
Cash, Cash Equivalents, and Restricted Cash, beginning of period	17,096	12,070	15,311
Cash, Cash Equivalents, and Restricted Cash, end of period	$ 18,762	$ 17,096	$ 12,070