BALANCE SHEETS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Document Fiscal Year Focus	2020
Property, plant and equipment
Property, plant and equipment	$ 6,536,625	$ 6,433,119
Accumulated depreciation and amortization	1,901,738	1,867,893
Net property, plant and equipment	4,634,887	4,565,226
Current assets
Cash and cash equivalents	11,069	17,853
Accounts receivable, net	234,327	260,012
Materials and supplies	53,390	55,732
Natural gas in storage	48,032	104,259
Regulatory assets	39,808	47,440
Other current assets	21,041	20,906
Total current assets	407,667	506,202
Goodwill and other assets
Regulatory assets	380,686	391,036
Goodwill	157,953	157,953
Other assets	93,712	87,883
Total goodwill and other assets	632,351	636,872
Total assets	5,674,905	5,708,300
Equity and long-term debt
Common stock, $0.01 par value: authorized 250,000,000 shares; issued and outstanding 52,736,623 shares at September 30, 2019; issued 52,598,005 and outstanding 52,564,902 shares at December 31, 2018	529	528
Paid-in Capital	1,729,587	1,733,092
Retained earnings	465,411	402,509
Accumulated other comprehensive loss	(6,515)	(6,739)
Total equity	2,189,012	2,129,390
Long-term debt, excluding current maturities and net issuance costs of $11,048 and $11,457, respectively	1,286,193	1,286,064
Total equity and long-term debt	3,475,205	3,415,454
Commercial Paper	474,695	516,500
Current liabilities
Accounts payable	82,088	120,490
Accrued taxes other than income	46,774	47,956
Regulatory Liability, Current	33,649	45,201
Customer deposits	58,272	57,987
Other current liabilities	80,675	84,603
Total current liabilities	776,153	872,737
Deferred credits and other liabilities
Deferred income taxes	698,877	682,632
Regulatory Liability, Noncurrent	494,210	503,518
Employee benefit obligations	109,865	115,657
Other deferred credits	120,595	118,302
Total deferred credits and other liabilities	1,423,547	1,420,109
Commitments and contingencies
Total liabilities and equity	5,674,905	5,708,300
Over-recovered purchased-gas costs [Member]
Current liabilities
Regulatory Liability, Current	27,367	27,623
Deferred credits and other liabilities
Regulatory Liability, Noncurrent	$ 0	$ 0