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Accounts Receivable-Related Parties (Narrative) (Details) (USD $) |  |  |  | 0 Months Ended |  |  | 12 Months Ended | 0 Months Ended | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Mar. 01, 2008 Wexford [Member] | Dec. 31, 2011 Charles E. Davidson [Member] | Sep. 28, 2012 Charles E. Davidson [Member] Maximum [Member] | Dec. 31, 2011 Orange Leaf Holdings, LLC [Member] Other Income (Expense) [Member] | Dec. 31, 2010 Orange Leaf Holdings, LLC [Member] Other Income (Expense) [Member] | Jul. 02, 2008 Everest Operations Management LLC [Member] | Mar. 31, 2012 Everest Operations Management LLC [Member] | Dec. 31, 2012 Everest Operations Management LLC [Member] | Dec. 31, 2011 Everest Operations Management LLC [Member] | Dec. 31, 2010 Everest Operations Management LLC [Member] | Jul. 01, 2008 Everest Operations Management LLC [Member] | Apr. 01, 2010 Windsor Niobrara LLC [Member]
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 |  |

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- Definition The aggregate amount of receivables to be collected from related parties where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth, at the financial statement date. which are usually due within one year (or one business cycle). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3(a)(2)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(k)(1)) -URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 57 -Paragraph 2 -Subparagraph d -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Subparagraph a -Article 5 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6361293&loc=d3e6676-107765 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph k -Subparagraph 2 -Article 4 + Details
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