BALANCE SHEETS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Document Fiscal Year Focus	2020
Property, plant and equipment
Property, plant and equipment	$ 6,633,738	$ 6,433,119
Accumulated depreciation and amortization	1,926,013	1,867,893
Net property, plant and equipment	4,707,725	4,565,226
Current assets
Cash and cash equivalents	10,454	17,853
Accounts receivable, net	138,885	260,012
Materials and supplies	54,586	55,732
Natural gas in storage	72,192	104,259
Regulatory assets	47,961	47,440
Other current assets	23,311	20,906
Total current assets	347,389	506,202
Goodwill and other assets
Regulatory assets	373,241	391,036
Goodwill	157,953	157,953
Other assets	95,304	87,883
Total goodwill and other assets	626,498	636,872
Total assets	5,681,612	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	529	528
Paid-in Capital	1,735,788	1,733,092
Retained earnings	461,962	402,509
Accumulated other comprehensive loss	(6,292)	(6,739)
Total equity	2,191,987	2,129,390
Long-term debt, excluding current maturities and net issuance costs of $13,540 and $10,936, respectively	1,581,931	1,286,064
Total equity and long-term debt	3,773,918	3,415,454
Commercial Paper	230,500	516,500
Current liabilities
Accounts payable	62,710	120,490
Accrued taxes other than income	41,922	47,956
Regulatory Liability, Current	26,163	45,201
Customer deposits	56,949	57,987
Other current liabilities	72,511	84,603
Total current liabilities	490,755	872,737
Deferred credits and other liabilities
Deferred income taxes	637,975	682,632
Regulatory Liability, Noncurrent	558,115	503,518
Employee benefit obligations	104,075	115,657
Other deferred credits	116,774	118,302
Total deferred credits and other liabilities	1,416,939	1,420,109
Commitments and contingencies
Total liabilities and equity	5,681,612	5,708,300
Over-recovered purchased-gas costs [Member]
Current liabilities
Regulatory Liability, Current	23,898	27,623
Deferred credits and other liabilities
Regulatory Liability, Noncurrent	$ 0	$ 0