2.4.0.81180 - Disclosure - Subsequent Eventstruefalsefalse1false falsefalseD2013Q2YTDhttp://www.sec.gov/CIK0001166036duration2013-01-01T00:00:002013-06-30T00:00:001true 1us-gaap_SubsequentEventsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Subsequent Events2false 2us-gaap_SubsequentEventsTextBlockus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00<div style="font-size:10.0pt;font-family:Times New Roman;"> 18. Subsequent Events   Approximately four million Class B units converted to common units on July 1, 2013.  These converted units will participate in the distributions declared on July 24, 2013.  All of the Partnership’s Class B units were issued to and are held by M&R MWE Liberty, LLC, an affiliate of The Energy and Minerals Group (“EMG”), as part of the Company’s December 31, 2011 acquisition of the non-controlling interest in MarkWest Liberty Midstream & Resources, L.L.C. (“MarkWest Liberty Midstream”). The remaining Class B units will convert to common units on a one-for-one basis in four equal installments beginning on July 1, 2014 and each of the next three anniversaries of such date.   </div>falsefalsefalsenonnum:textBlockItemTypenaThe entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.No definition available.false0Subsequent EventsfalseSubsequent EventsUnKnownUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.markwest.com/role/DisclosureSubsequentEvents12