2.4.0.84150 - Disclosure - Segment Information (Details)truefalseIn Thousands, unless otherwise specifiedfalse1false USDfalsefalse$D2013Q2http://www.sec.gov/CIK0001166036duration2013-04-01T00:00:002013-06-30T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2false USDfalsefalse$D2012Q2http://www.sec.gov/CIK0001166036duration2012-04-01T00:00:002012-06-30T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$3false USDfalsefalse$D2013Q2YTDhttp://www.sec.gov/CIK0001166036duration2013-01-01T00:00:002013-06-30T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$4false USDfalsefalse$D2012Q2YTDhttp://www.sec.gov/CIK0001166036duration2012-01-01T00:00:002012-06-30T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$1true 3us-gaap_SegmentReportingInformationLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Segment information2false 4us-gaap_GasGatheringTransportationMarketingAndProcessingRevenueus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse395421000395421USD$falsetruefalse2truefalsefalse306755000306755USD$falsetruefalse3truefalsefalse768879000768879USD$falsetruefalse4truefalsefalse702733000702733USD$falsetruefalsexbrli:monetaryItemTypemonetaryRevenue related to midstream and downstream gas activities. May include the following: gathering from wells, processing to remove impurities, storage, transmission, and the sale of natural gas and related products.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62246-109447 false2Revenue3false 4us-gaap_NaturalGasMidstreamCostsus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse155359000155359USD$falsefalsefalse2truefalsefalse112731000112731USD$falsefalsefalse3truefalsefalse307916000307916USD$falsefalsefalse4truefalsefalse267286000267286USD$falsefalsefalsexbrli:monetaryItemTypemonetaryMidstream costs of residue gas, natural gas liquids and condensate. Midstream is a term sometimes used to identify those industry activities that fall between exploration and production (upstream) and refining and marketing (downstream). The term is most often applied to pipeline transportation of crude oil and natural gas.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 false2Purchased product costs4false 4us-gaap_FacilityCostsus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse6279700062797USD$falsefalsefalse2truefalsefalse4823000048230USD$falsefalsefalse3truefalsefalse122307000122307USD$falsefalsefalse4truefalsefalse9655500096555USD$falsefalsefalsexbrli:monetaryItemTypemonetaryFacility expenses incurred related to gas and oil produced and sold during the reporting period.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 false2Facility expenses5false 4us-gaap_OperatingIncomeLossus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse140022000140022USD$falsefalsefalse2truefalsefalse257741000257741USD$falsefalsefalse3truefalsefalse203685000203685USD$falsefalsefalse4truefalsefalse308233000308233USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe net result for the period of deducting operating expenses from operating revenues.No definition available.true2Income from operations6false 4us-gaap_PaymentsToAcquirePropertyPlantAndEquipmentus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3truefalsefalse14350840001435084USD$falsefalsefalse4truefalsefalse580980000580980USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3213-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 17 -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Capital expenditures7false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse5false USDtruefalse$D2013Q2_ReportableSegmentsMemberhttp://www.sec.gov/CIK0001166036duration2013-04-01T00:00:002013-06-30T00:00:00falsefalseTotal reportable segmentsus-gaap_StatementGeographicalAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_ReportableSegmentsMemberus-gaap_StatementGeographicalAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Total reportable segments8true 3us-gaap_SegmentReportingInformationLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Segment information9false 4us-gaap_GasGatheringTransportationMarketingAndProcessingRevenueus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse396858000396858USD$falsefalsefalse2truefalsefalse308079000308079USD$falsefalsefalse3truefalsefalse771680000771680USD$falsefalsefalse4truefalsefalse705950000705950USD$falsefalsefalsexbrli:monetaryItemTypemonetaryRevenue related to midstream and downstream gas activities. May include the following: gathering from wells, processing to remove impurities, storage, transmission, and the sale of natural gas and related products.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62246-109447 false2Revenue10false 4us-gaap_NaturalGasMidstreamCostsus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse155359000155359USD$falsefalsefalse2truefalsefalse112731000112731USD$falsefalsefalse3truefalsefalse307916000307916USD$falsefalsefalse4truefalsefalse267286000267286USD$falsefalsefalsexbrli:monetaryItemTypemonetaryMidstream costs of residue gas, natural gas liquids and condensate. Midstream is a term sometimes used to identify those industry activities that fall between exploration and production (upstream) and refining and marketing (downstream). The term is most often applied to pipeline transportation of crude oil and natural gas.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 false2Purchased product costs11false 4mwe_NetOperatingMarginmwe_falsecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse241499000241499USD$falsefalsefalse2truefalsefalse195348000195348USD$falsefalsefalse3truefalsefalse463764000463764USD$falsefalsefalse4truefalsefalse438664000438664USD$falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the net operating margin which is defined as segment revenue, excluding any derivative gain (loss) and adjusted for the non-cash impact of revenue deferrals related to certain agreements, less purchased product costs, excluding any derivative gain (loss).No definition available.true2Net operating margin12false 4us-gaap_FacilityCostsus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse6511700065117USD$falsefalsefalse2truefalsefalse5073500050735USD$falsefalsefalse3truefalsefalse126929000126929USD$falsefalsefalse4truefalsefalse101298000101298USD$falsefalsefalsexbrli:monetaryItemTypemonetaryFacility expenses incurred related to gas and oil produced and sold during the reporting period.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 false2Facility expenses13false 4mwe_MinorityInterestInOperatingIncomeLossLimitedPartnershipsmwe_falsedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse-1090000-1090USD$falsefalsefalse2truefalsefalse-85000-85USD$falsefalsefalse3truefalsefalse-2365000-2365USD$falsefalsefalse4truefalsefalse-82000-82USD$falsefalsefalsexbrli:monetaryItemTypemonetaryAmount of operating income or loss attributable to the reportable segments for the period that is attributable to the non-controlling partners of the entity's less than wholly-owned subsidiaries.No definition available.false2Portion of operating income (loss) attributable to non-controlling interests14false 4us-gaap_OperatingIncomeLossus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse177472000177472USD$falsefalsefalse2truefalsefalse144698000144698USD$falsefalsefalse3truefalsefalse339200000339200USD$falsefalsefalse4truefalsefalse337448000337448USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe net result for the period of deducting operating expenses from operating revenues.No definition available.true2Income from operations15false 4us-gaap_PaymentsToAcquirePropertyPlantAndEquipmentus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3truefalsefalse14301840001430184USD$falsefalsefalse4truefalsefalse577248000577248USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3213-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 17 -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Capital expenditures16false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse9false USDtruefalse$D2013Q2_LibertyMemberhttp://www.sec.gov/CIK0001166036duration2013-04-01T00:00:002013-06-30T00:00:00falsefalseLiberty Segmentus-gaap_StatementGeographicalAxisxbrldihttp://xbrl.org/2006/xbrldimwe_LibertyMemberus-gaap_StatementGeographicalAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Liberty Segment17true 3us-gaap_SegmentReportingInformationLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Segment information18false 4us-gaap_GasGatheringTransportationMarketingAndProcessingRevenueus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse120057000120057USD$falsefalsefalse2truefalsefalse5947700059477USD$falsefalsefalse3truefalsefalse228554000228554USD$falsefalsefalse4truefalsefalse135054000135054USD$falsefalsefalsexbrli:monetaryItemTypemonetaryRevenue related to midstream and downstream gas activities. May include the following: gathering from wells, processing to remove impurities, storage, transmission, and the sale of natural gas and related products.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62246-109447 false2Revenue19false 4us-gaap_NaturalGasMidstreamCostsus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse1699300016993USD$falsefalsefalse2truefalsefalse80180008018USD$falsefalsefalse3truefalsefalse3578600035786USD$falsefalsefalse4truefalsefalse3265300032653USD$falsefalsefalsexbrli:monetaryItemTypemonetaryMidstream costs of residue gas, natural gas liquids and condensate. Midstream is a term sometimes used to identify those industry activities that fall between exploration and production (upstream) and refining and marketing (downstream). The term is most often applied to pipeline transportation of crude oil and natural gas.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 false2Purchased product costs20false 4mwe_NetOperatingMarginmwe_falsecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse103064000103064USD$falsefalsefalse2truefalsefalse5145900051459USD$falsefalsefalse3truefalsefalse192768000192768USD$falsefalsefalse4truefalsefalse102401000102401USD$falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the net operating margin which is defined as segment revenue, excluding any derivative gain (loss) and adjusted for the non-cash impact of revenue deferrals related to certain agreements, less purchased product costs, excluding any derivative gain (loss).No definition available.true2Net operating margin21false 4us-gaap_FacilityCostsus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse2227200022272USD$falsefalsefalse2truefalsefalse1336400013364USD$falsefalsefalse3truefalsefalse4490800044908USD$falsefalsefalse4truefalsefalse2561100025611USD$falsefalsefalsexbrli:monetaryItemTypemonetaryFacility expenses incurred related to gas and oil produced and sold during the reporting period.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 false2Facility expenses22false 4us-gaap_OperatingIncomeLossus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse8079200080792USD$falsefalsefalse2truefalsefalse3809500038095USD$falsefalsefalse3truefalsefalse147860000147860USD$falsefalsefalse4truefalsefalse7679000076790USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe net result for the period of deducting operating expenses from operating revenues.No definition available.true2Income from operations23false 4us-gaap_PaymentsToAcquirePropertyPlantAndEquipmentus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3truefalsefalse729040000729040USD$falsefalsefalse4truefalsefalse415506000415506USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3213-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 17 -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Capital expenditures24false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse13false USDtruefalse$D2013Q2_UticaMemberhttp://www.sec.gov/CIK0001166036duration2013-04-01T00:00:002013-06-30T00:00:00falsefalseUtica Segmentus-gaap_StatementGeographicalAxisxbrldihttp://xbrl.org/2006/xbrldimwe_UticaMemberus-gaap_StatementGeographicalAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Utica Segment25true 3us-gaap_SegmentReportingInformationLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Segment information26false 4us-gaap_GasGatheringTransportationMarketingAndProcessingRevenueus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse35940003594USD$falsefalsefalse2falsefalsefalse00falsefalsefalse3truefalsefalse42170004217USD$falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryRevenue related to midstream and downstream gas activities. May include the following: gathering from wells, processing to remove impurities, storage, transmission, and the sale of natural gas and related products.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62246-109447 false2Revenue27false 4mwe_NetOperatingMarginmwe_falsecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse35940003594USD$falsefalsefalse2falsefalsefalse00falsefalsefalse3truefalsefalse42170004217USD$falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the net operating margin which is defined as segment revenue, excluding any derivative gain (loss) and adjusted for the non-cash impact of revenue deferrals related to certain agreements, less purchased product costs, excluding any derivative gain (loss).No definition available.true2Net operating margin28false 4us-gaap_FacilityCostsus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse64120006412USD$falsefalsefalse2truefalsefalse283000283USD$falsefalsefalse3truefalsefalse1037400010374USD$falsefalsefalse4truefalsefalse283000283USD$falsefalsefalsexbrli:monetaryItemTypemonetaryFacility expenses incurred related to gas and oil produced and sold during the reporting period.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 false2Facility expenses29false 4mwe_MinorityInterestInOperatingIncomeLossLimitedPartnershipsmwe_falsedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse-1143000-1143USD$falsefalsefalse2truefalsefalse-113000-113USD$falsefalsefalse3truefalsefalse-2482000-2482USD$falsefalsefalse4truefalsefalse-113000-113USD$falsefalsefalsexbrli:monetaryItemTypemonetaryAmount of operating income or loss attributable to the reportable segments for the period that is attributable to the non-controlling partners of the entity's less than wholly-owned subsidiaries.No definition available.false2Portion of operating income (loss) attributable to non-controlling interests30false 4us-gaap_OperatingIncomeLossus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse-1675000-1675USD$falsefalsefalse2truefalsefalse-170000-170USD$falsefalsefalse3truefalsefalse-3675000-3675USD$falsefalsefalse4truefalsefalse-170000-170USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe net result for the period of deducting operating expenses from operating revenues.No definition available.true2Income from operations31false 4us-gaap_PaymentsToAcquirePropertyPlantAndEquipmentus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3truefalsefalse640819000640819USD$falsefalsefalse4truefalsefalse1678600016786USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3213-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 17 -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Capital expenditures32false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse17false USDtruefalse$D2013Q2_NortheastMemberhttp://www.sec.gov/CIK0001166036duration2013-04-01T00:00:002013-06-30T00:00:00falsefalseNortheast Segmentus-gaap_StatementGeographicalAxisxbrldihttp://xbrl.org/2006/xbrldimwe_NortheastMemberus-gaap_StatementGeographicalAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Northeast Segment33true 3us-gaap_SegmentReportingInformationLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Segment information34false 4us-gaap_GasGatheringTransportationMarketingAndProcessingRevenueus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse4536500045365USD$falsefalsefalse2truefalsefalse4205100042051USD$falsefalsefalse3truefalsefalse102701000102701USD$falsefalsefalse4truefalsefalse128969000128969USD$falsefalsefalsexbrli:monetaryItemTypemonetaryRevenue related to midstream and downstream gas activities. May include the following: gathering from wells, processing to remove impurities, storage, transmission, and the sale of natural gas and related products.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62246-109447 false2Revenue35false 4us-gaap_NaturalGasMidstreamCostsus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse1512600015126USD$falsefalsefalse2truefalsefalse1292100012921USD$falsefalsefalse3truefalsefalse3478800034788USD$falsefalsefalse4truefalsefalse3860800038608USD$falsefalsefalsexbrli:monetaryItemTypemonetaryMidstream costs of residue gas, natural gas liquids and condensate. Midstream is a term sometimes used to identify those industry activities that fall between exploration and production (upstream) and refining and marketing (downstream). The term is most often applied to pipeline transportation of crude oil and natural gas.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 false2Purchased product costs36false 4mwe_NetOperatingMarginmwe_falsecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse3023900030239USD$falsefalsefalse2truefalsefalse2913000029130USD$falsefalsefalse3truefalsefalse6791300067913USD$falsefalsefalse4truefalsefalse9036100090361USD$falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the net operating margin which is defined as segment revenue, excluding any derivative gain (loss) and adjusted for the non-cash impact of revenue deferrals related to certain agreements, less purchased product costs, excluding any derivative gain (loss).No definition available.true2Net operating margin37false 4us-gaap_FacilityCostsus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse66550006655USD$falsefalsefalse2truefalsefalse49320004932USD$falsefalsefalse3truefalsefalse1317900013179USD$falsefalsefalse4truefalsefalse1131000011310USD$falsefalsefalsexbrli:monetaryItemTypemonetaryFacility expenses incurred related to gas and oil produced and sold during the reporting period.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 false2Facility expenses38false 4us-gaap_OperatingIncomeLossus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse2358400023584USD$falsefalsefalse2truefalsefalse2419800024198USD$falsefalsefalse3truefalsefalse5473400054734USD$falsefalsefalse4truefalsefalse7905100079051USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe net result for the period of deducting operating expenses from operating revenues.No definition available.true2Income from operations39false 4us-gaap_PaymentsToAcquirePropertyPlantAndEquipmentus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3truefalsefalse25090002509USD$falsefalsefalse4truefalsefalse4347500043475USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3213-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 17 -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Capital expenditures40false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse21false USDtruefalse$D2013Q2_SouthwestMemberhttp://www.sec.gov/CIK0001166036duration2013-04-01T00:00:002013-06-30T00:00:00falsefalseSouthwest Segmentus-gaap_StatementGeographicalAxisxbrldihttp://xbrl.org/2006/xbrldimwe_SouthwestMemberus-gaap_StatementGeographicalAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Southwest Segment41true 3us-gaap_SegmentReportingInformationLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Segment information42false 4us-gaap_GasGatheringTransportationMarketingAndProcessingRevenueus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse227842000227842USD$falsefalsefalse2truefalsefalse206551000206551USD$falsefalsefalse3truefalsefalse436208000436208USD$falsefalsefalse4truefalsefalse441927000441927USD$falsefalsefalsexbrli:monetaryItemTypemonetaryRevenue related to midstream and downstream gas activities. May include the following: gathering from wells, processing to remove impurities, storage, transmission, and the sale of natural gas and related products.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62246-109447 false2Revenue43false 4us-gaap_NaturalGasMidstreamCostsus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse123240000123240USD$falsefalsefalse2truefalsefalse9179200091792USD$falsefalsefalse3truefalsefalse237342000237342USD$falsefalsefalse4truefalsefalse196025000196025USD$falsefalsefalsexbrli:monetaryItemTypemonetaryMidstream costs of residue gas, natural gas liquids and condensate. Midstream is a term sometimes used to identify those industry activities that fall between exploration and production (upstream) and refining and marketing (downstream). The term is most often applied to pipeline transportation of crude oil and natural gas.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 false2Purchased product costs44false 4mwe_NetOperatingMarginmwe_falsecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse104602000104602USD$falsefalsefalse2truefalsefalse114759000114759USD$falsefalsefalse3truefalsefalse198866000198866USD$falsefalsefalse4truefalsefalse245902000245902USD$falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the net operating margin which is defined as segment revenue, excluding any derivative gain (loss) and adjusted for the non-cash impact of revenue deferrals related to certain agreements, less purchased product costs, excluding any derivative gain (loss).No definition available.true2Net operating margin45false 4us-gaap_FacilityCostsus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse2977800029778USD$falsefalsefalse2truefalsefalse3215600032156USD$falsefalsefalse3truefalsefalse5846800058468USD$falsefalsefalse4truefalsefalse6409400064094USD$falsefalsefalsexbrli:monetaryItemTypemonetaryFacility expenses incurred related to gas and oil produced and sold during the reporting period.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 false2Facility expenses46false 4mwe_MinorityInterestInOperatingIncomeLossLimitedPartnershipsmwe_falsedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse5300053USD$falsefalsefalse2truefalsefalse2800028USD$falsefalsefalse3truefalsefalse117000117USD$falsefalsefalse4truefalsefalse3100031USD$falsefalsefalsexbrli:monetaryItemTypemonetaryAmount of operating income or loss attributable to the reportable segments for the period that is attributable to the non-controlling partners of the entity's less than wholly-owned subsidiaries.No definition available.false2Portion of operating income (loss) attributable to non-controlling interests47false 4us-gaap_OperatingIncomeLossus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse7477100074771USD$falsefalsefalse2truefalsefalse8257500082575USD$falsefalsefalse3truefalsefalse140281000140281USD$falsefalsefalse4truefalsefalse181777000181777USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe net result for the period of deducting operating expenses from operating revenues.No definition available.true2Income from operations48false 4us-gaap_PaymentsToAcquirePropertyPlantAndEquipmentus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3truefalsefalse5781600057816USD$falsefalsefalse4truefalsefalse101481000101481USD$falsefalsefalsexbrli:monetaryItemTypemonetaryThe cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3213-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 17 -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Capital expenditures49false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse25false USDtruefalse$D2013Q2YTD_UnallocatedAmountToSegmentMemberhttp://www.sec.gov/CIK0001166036duration2013-01-01T00:00:002013-06-30T00:00:00falsefalseUnallocated Segmentus-gaap_StatementGeographicalAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_UnallocatedAmountToSegmentMemberus-gaap_StatementGeographicalAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Unallocated Segment50true 3us-gaap_SegmentReportingInformationLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Segment information51false 4us-gaap_PaymentsToAcquirePropertyPlantAndEquipmentus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3truefalsefalse49000004900USD$falsetruefalse4truefalsefalse37320003732USD$falsetruefalsexbrli:monetaryItemTypemonetaryThe cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3213-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 17 -Subparagraph c -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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 -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. false2Capital expendituresfalseSegment Information (Details) (USD $)ThousandsUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.markwest.com/role/DisclosureSegmentInformationDetails451