BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Property, plant and equipment
Property, plant and equipment	$ 4,904,206	$ 4,850,201
Accumulated depreciation and amortization	1,578,438	1,556,481
Net property, plant and equipment	3,325,768	3,293,720
Current assets
Cash and cash equivalents	142,502	11,943
Accounts receivable, net	308,850	326,749
Income tax receivable	5,590	43,800
Natural gas in storage	81,277	185,300
Regulatory assets (Note 2)	22,322	50,193
Other current assets	43,903	49,516
Total current assets	604,444	667,501
Goodwill and other assets
Regulatory assets (Note 2)	465,049	478,723
Goodwill	157,953	157,953
Other assets	52,274	51,313
Total goodwill and other assets	675,276	687,989
Total assets	4,605,488	4,649,210
Equity and long-term debt
Common stock, $0.01 par value: authorized 250,000,000 shares; issued and outstanding 52,590,112 shares at March 31, 2015; issued and outstanding 52,083,859 at December 31, 2014	526	521
Paid-in Capital	1,759,934	1,758,796
Retained earnings	84,239	39,894
Accumulated other comprehensive income (loss)	(5,034)	(5,174)
Total equity	1,839,665	1,794,037
Long-term debt, excluding current maturities	1,201,310	1,201,311
Total equity and long-term debt	3,040,975	2,995,348
Current liabilities
Current maturities of long-term debt	6	6
Notes payable	0	42,000
Accounts payable	105,058	159,064
Accrued taxes other than income	47,859	44,742
Accrued liabilities	13,648	26,019
Customer deposits	60,856	60,003
Regulatory liabilities	54,252	32,467
Other current liabilities	18,324	28,132
Total current liabilities	300,003	392,433
Deferred credits and other liabilities [Abstract]
Deferred income taxes	897,458	894,585
Employee benefit obligations	286,654	287,779
Other deferred credits	80,398	79,065
Total deferred credits and other liabilities	1,264,510	1,261,429
Commitments and contingencies (Note 8)
Total liabilities and equity	$ 4,605,488	$ 4,649,210