BALANCE SHEETS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Document Fiscal Year Focus	2019
Property, plant and equipment
Property, plant and equipment	$ 6,336,041	$ 6,073,143
Accumulated depreciation and amortization	1,847,573	1,789,431
Net property, plant and equipment	4,488,468	4,283,712
Current assets
Cash and cash equivalents	12,562	21,323
Accounts receivable, net	130,768	295,421
Materials and supplies	56,788	44,333
Natural gas in storage	118,450	107,295
Regulatory assets	54,123	54,420
Other current assets	16,992	20,495
Total current assets	389,683	543,287
Goodwill and other assets
Regulatory assets	416,140	437,479
Goodwill	157,953	157,953
Other assets	80,936	46,211
Total goodwill and other assets	655,029	641,643
Total assets	5,533,180	5,468,642
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	527	526
Paid-in Capital	1,728,237	1,727,492
Retained earnings	377,941	320,869
Accumulated other comprehensive loss	(4,824)	(4,086)
Treasury stock, at cost: 33,103 shares at December 31, 2018	0	(2,145)
Total equity	2,101,881	2,042,656
Long-term debt, excluding current maturities and net issuance costs of $11,048 and $11,457, respectively	1,285,937	1,285,483
Total equity and long-term debt	3,387,818	3,328,139
Current liabilities
Notes payable	395,000	299,500
Accounts payable	62,575	174,510
Accrued taxes other than income	47,205	47,640
Regulatory Liability, Current	48,784	48,394
Customer deposits	57,531	61,183
Other current liabilities	66,660	67,664
Total current liabilities	677,755	698,891
Deferred credits and other liabilities
Deferred income taxes	675,613	652,426
Regulatory Liability, Noncurrent	506,961	520,866
Employee benefit obligations	164,206	178,720
Other deferred credits	120,827	89,600
Total deferred credits and other liabilities	1,467,607	1,441,612
Commitments and contingencies
Total liabilities and equity	5,533,180	5,468,642
Over-recovered purchased-gas costs [Member]
Current liabilities
Regulatory Liability, Current	27,543	13,668
Deferred credits and other liabilities
Regulatory Liability, Noncurrent	$ 0	$ 0