BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Property, plant and equipment
Property, plant and equipment	$ 5,196,788	$ 5,132,682
Accumulated depreciation and amortization	1,639,054	1,620,771
Net property, plant and equipment	3,557,734	3,511,911
Current assets
Cash and cash equivalents	52,657	2,433
Accounts receivable, net	195,158	216,343
Materials and supplies	29,708	33,325
Income tax receivable	0	38,877
Natural gas in storage	80,553	142,153
Regulatory assets	42,741	32,925
Other current assets	16,794	16,789
Total current assets	417,611	482,845
Goodwill and other assets
Regulatory assets	421,559	435,863
Goodwill	157,953	157,953
Other assets	43,247	46,193
Total goodwill and other assets	622,759	640,009
Total assets	4,598,104	4,634,765
Equity and long-term debt
Common stock, $0.01 par value: authorized 250,000,000 shares; issued 52,598,005 shares and outstanding 52,161,588 shares at March 31, 2016; issued 52,598,005 and outstanding 52,259,224 at December 31, 2015	526	526
Paid-in Capital	1,754,899	1,764,875
Retained earnings	141,180	95,046
Accumulated other comprehensive income (loss)	(4,285)	(4,401)
Treasury stock, at cost: 436,417 shares at March 31, 2016 and 338,781 shares at December 31, 2015	25,133	14,491
Total equity	1,867,187	1,841,555
Long-term debt, excluding current maturities and net issuance costs of $9,449 and $9,645, respectively	1,191,854	1,191,660
Total equity and long-term debt	3,059,041	3,033,215
Current liabilities
Current maturities of long-term debt	7	7
Notes payable	0	12,500
Accounts payable	59,887	107,482
Accrued interest	7,654	18,873
Accrued taxes other than income	37,784	37,249
Accrued liabilities	15,000	31,470
Customer deposits	62,423	60,325
Regulatory liabilities	20,089	24,615
Other current liabilities	25,749	11,700
Total current liabilities	228,593	304,221
Deferred credits and other liabilities [Abstract]
Deferred income taxes	967,943	951,785
Employee benefit obligations	268,081	272,309
Other deferred credits	74,446	73,235
Total deferred credits and other liabilities	$ 1,310,470	$ 1,297,329
Commitments and contingencies
Total liabilities and equity	$ 4,598,104	$ 4,634,765