BALANCE SHEETS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Document Fiscal Year Focus	2019
Property, plant and equipment
Property, plant and equipment	$ 6,241,105	$ 6,073,143
Accumulated depreciation and amortization	1,840,457	1,789,431
Net property, plant and equipment	4,400,648	4,283,712
Current assets
Cash and cash equivalents	11,114	21,323
Accounts receivable, net	169,801	295,421
Materials and supplies	50,344	44,333
Natural gas in storage	88,235	107,295
Regulatory assets	38,372	54,420
Other current assets	18,946	20,495
Total current assets	376,812	543,287
Goodwill and other assets
Regulatory assets	424,304	437,479
Goodwill	157,953	157,953
Other assets	86,889	46,211
Total goodwill and other assets	669,146	641,643
Total assets	5,446,606	5,468,642
Equity and long-term debt
Common stock, $0.01 par value: authorized 250,000,000 shares; issued and outstanding 52,734,222 shares at June 30, 2019; issued 52,598,005 and outstanding 52,564,902 shares at December 31, 2018	527	526
Paid-in Capital	1,725,843	1,727,492
Retained earnings	387,077	320,869
Accumulated other comprehensive loss	(4,984)	(4,086)
Treasury stock, at cost: 33,103 shares at December 31, 2018	0	(2,145)
Total equity	2,108,463	2,042,656
Long-term debt, excluding current maturities and net issuance costs of $11,159 and $11,457, respectively	1,285,811	1,285,483
Total equity and long-term debt	3,394,274	3,328,139
Current liabilities
Notes payable	293,000	299,500
Accounts payable	67,578	174,510
Accrued taxes other than income	37,312	47,640
Regulatory Liability, Current	46,534	48,394
Customer deposits	58,831	61,183
Other current liabilities	75,098	67,664
Total current liabilities	578,353	698,891
Deferred credits and other liabilities
Deferred income taxes	673,939	652,426
Regulatory Liability, Noncurrent	508,877	520,866
Employee benefit obligations	168,387	178,720
Other deferred credits	122,776	89,600
Total deferred credits and other liabilities	1,473,979	1,441,612
Commitments and contingencies
Total liabilities and equity	5,446,606	5,468,642
Over-recovered purchased-gas costs [Member]
Current liabilities
Regulatory Liability, Current	22,616	13,668
Deferred credits and other liabilities
Regulatory Liability, Noncurrent	$ 0	$ 0