STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating activities
Net income	$ 206,434	$ 196,412	$ 186,749
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	207,233	194,881	180,395
Deferred income taxes	43,449	18,485	13,307
Share-based compensation expense	10,498	9,803	9,314
Provision for doubtful accounts	9,131	15,450	8,994
Changes in assets and liabilities:
Accounts receivable	(57,902)	(58,423)	30,415
Materials and supplies	(2,126)	2,966	(11,399)
Natural gas in storage	(85,700)	10,313	3,036
Asset removal costs	(49,029)	(40,833)	(47,784)
Accounts payable	107,207	28,376	(59,293)
Accrued taxes other than income	3,235	15,844	316
Customer deposits	(5,574)	10,041	(3,196)
Increase Decrease In Regulatory Assets And Liabilities Current	(1,562,574)	(38,773)	3,787
Increase Decrease In Regulatory Assets And Liabilities Non-current	(367,210)	23,648	24,416
Employee benefit obligation	0	(3,109)	(35,401)
Increase (Decrease) in Other Current Assets and Liabilities, Net	18,461	(12,877)	7,173
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net	(11,190)	(7,704)	(484)
Cash provided by operating activities	(1,535,657)	364,500	310,345
Investing activities
Capital expenditures	(495,246)	(471,345)	(417,322)
Payments to Acquire Assets, Investing Activities	(7,554)	(2,804)	(7,009)
Proceeds from Sale of Other Assets, Investing Activities	1,717	3,777	1,399
Cash used in investing activities	(501,083)	(470,372)	(422,932)
Financing activities
Borrowings (repayment) on notes payable, net	75,775	(98,275)	217,000
Proceeds from Issuance of Long-term Debt	2,498,895	298,428	0
Payments of Financing Costs	(35,110)	(2,885)	0
Issuance of common stock	26,662	19,383	5,116
Repayments of Long-term Debt	(400,000)	0	0
Dividends paid	(123,912)	(114,372)	(105,424)
Tax withholdings related to net share settlements of stock compensation	(4,711)	(6,267)	(7,575)
Cash provided by (used in) financing activities	2,037,599	96,012	109,117
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect, Total	859	(9,860)	(3,470)
Cash and cash equivalents at beginning of period	7,993	17,853	21,323
Cash and cash equivalents at end of period	8,852	7,993	17,853
Supplemental cash flow information:
Interest Paid, Excluding Capitalized Interest, Operating Activities	70,066	60,126	61,160
Cash received for income taxes, net	$ (10,809)	$ 30,361	$ 30,152