Schedule of Held-for-sale Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	$ 130,743	$ 0
Total liabilities held-for-sale	(7,917)	0
Total held-for-sale properties	122,826
Accounts receivable
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	5,257
Inventories
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	286
Oil and gas properties
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	294,607
Less accumulated depreciation, depletion and amortization
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	(172,464)
Utility plant
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	7,971
Less accumulated depreciation
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	(4,960)
Other property, net
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	46
Accounts payable
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total liabilities held-for-sale	(1,573)
Royalty payable
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total liabilities held-for-sale	(646)
Other current liabilities
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total liabilities held-for-sale	(266)
Total liabilities held-for-sale
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total liabilities held-for-sale	(5,432)
Oil and gas operations
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	127,732
Total liabilities held-for-sale	(7,917)
Total held-for-sale properties	119,815
Oil and gas operations | Accounts receivable
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	5,257
Oil and gas operations | Inventories
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	286
Oil and gas operations | Oil and gas properties
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	294,607
Oil and gas operations | Less accumulated depreciation, depletion and amortization
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	(172,464)
Oil and gas operations | Utility plant
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	0
Oil and gas operations | Less accumulated depreciation
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	0
Oil and gas operations | Other property, net
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	46
Oil and gas operations | Accounts payable
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total liabilities held-for-sale	(1,573)
Oil and gas operations | Royalty payable
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total liabilities held-for-sale	(646)
Oil and gas operations | Other current liabilities
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total liabilities held-for-sale	(266)
Oil and gas operations | Total liabilities held-for-sale
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total liabilities held-for-sale	(5,432)
Natural gas distribution
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	3,011
Total liabilities held-for-sale	0
Total held-for-sale properties	3,011
Natural gas distribution | Accounts receivable
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	0
Natural gas distribution | Inventories
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	0
Natural gas distribution | Oil and gas properties
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	0
Natural gas distribution | Less accumulated depreciation, depletion and amortization
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	0
Natural gas distribution | Utility plant
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	7,971
Natural gas distribution | Less accumulated depreciation
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	(4,960)
Natural gas distribution | Other property, net
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total assets held-for-sale	0
Natural gas distribution | Accounts payable
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total liabilities held-for-sale	0
Natural gas distribution | Royalty payable
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total liabilities held-for-sale	0
Natural gas distribution | Other current liabilities
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total liabilities held-for-sale	0
Natural gas distribution | Total liabilities held-for-sale
Schedule of Held-for-sale Assets and Liabilities [Line Items]
Total liabilities held-for-sale	$ 0