BALANCE SHEETS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Document Fiscal Year Focus	2020
Property, plant and equipment
Property, plant and equipment	$ 6,735,032	$ 6,433,119
Accumulated depreciation and amortization	1,955,200	1,867,893
Net property, plant and equipment	4,779,832	4,565,226
Current assets
Cash and cash equivalents	6,184	17,853
Accounts receivable, net	106,777	260,012
Materials and supplies	55,492	55,732
Natural gas in storage	105,377	104,259
Regulatory assets	71,748	47,440
Other current assets	24,126	20,906
Total current assets	369,704	506,202
Goodwill and other assets
Regulatory assets	364,117	391,036
Goodwill	157,953	157,953
Other assets	92,158	87,883
Total goodwill and other assets	614,228	636,872
Total assets	5,763,764	5,708,300
Equity and long-term debt
Common stock, $0.01 par value: authorized 250,000,000 shares; issued and outstanding 52,920,530 shares at June 30, 2020; issued and outstanding 52,771,749 shares at December 31, 2019	531	528
Paid-in Capital	1,751,350	1,733,092
Retained earnings	454,205	402,509
Accumulated other comprehensive loss	(6,069)	(6,739)
Total equity	2,200,017	2,129,390
Long-term debt, excluding current maturities and net issuance costs of $13,540 and $10,936, respectively	1,582,193	1,286,064
Total equity and long-term debt	3,782,210	3,415,454
Commercial Paper	308,000	516,500
Current liabilities
Accounts payable	65,311	120,490
Accrued taxes other than income	57,732	47,956
Regulatory Liability, Current	20,454	45,201
Customer deposits	55,319	57,987
Other current liabilities	68,898	84,603
Total current liabilities	575,714	872,737
Deferred credits and other liabilities
Deferred income taxes	642,309	682,632
Regulatory Liability, Noncurrent	555,258	503,518
Employee benefit obligations	98,257	115,657
Other deferred credits	110,016	118,302
Total deferred credits and other liabilities	1,405,840	1,420,109
Commitments and contingencies
Total liabilities and equity	$ 5,763,764	$ 5,708,300
Common stock, par value per share	$ 0.01	$ 0.01
Over-recovered purchased-gas costs [Member]
Current liabilities
Regulatory Liability, Current	$ 20,454	$ 27,623
Deferred credits and other liabilities
Regulatory Liability, Noncurrent	$ 0	$ 0