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Accounts Receivable-Related Parties (Narrative) (Details) (USD $)
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0 Months Ended | 12 Months Ended | 0 Months Ended | 3 Months Ended | 12 Months Ended | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Mar. 31, 2013
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Dec. 31, 2012
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Dec. 31, 2011
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Mar. 01, 2008
Wexford [Member]
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Dec. 31, 2011
Charles E. Davidson [Member]
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Sep. 28, 2012
Charles E. Davidson [Member]
Maximum [Member]
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Dec. 31, 2011
Orange Leaf Holdings, LLC [Member]
Other Income (Expense) [Member]
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Dec. 31, 2010
Orange Leaf Holdings, LLC [Member]
Other Income (Expense) [Member]
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Jul. 02, 2008
Everest Operations Management LLC [Member]
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Mar. 31, 2012
Everest Operations Management LLC [Member]
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Dec. 31, 2012
Everest Operations Management LLC [Member]
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Dec. 31, 2011
Everest Operations Management LLC [Member]
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Dec. 31, 2010
Everest Operations Management LLC [Member]
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Jul. 01, 2008
Everest Operations Management LLC [Member]
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Apr. 01, 2010
Windsor Niobrara LLC [Member]
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| Related Party Transaction [Line Items] | |||||||||||||||
| Accounts receivable-related parties | $ 37,062,000 | $ 34,848,000 | $ 4,731,000 | ||||||||||||
| Required notice term | 60 days | ||||||||||||||
| Required notice period, counterparty | 30 days | 30 days | |||||||||||||
| Breach of contract, cure period | 30 days | ||||||||||||||
| Ownership Of Company By Third Party | 13.30% | 1.00% | |||||||||||||
| Affiliates participation percentage in acquisition of leases | 50.00% | ||||||||||||||
| Rental income | 66,000 | 20,000 | |||||||||||||
| Percentage of proportionate share of acquisition or divestiture consideration payable to affiliates | 1.00% | ||||||||||||||
| Reimbursement for general and administrative expenses performed for related party under acquisition team agreement | $ 300,000 | $ 1,087,000 | $ 1,184,000 | $ 0 | |||||||||||