2.4.0.84101 - Disclosure - Commitments and Contingent Liabilities (Details 2)truefalseIn Millions, unless otherwise specifiedfalse1false USDfalsefalse$D2013Q2YTD_ObligationsUnderLloydsCentralFundMemberhttp://www.sec.gov/CIK0001165880duration2013-01-01T00:00:002013-06-30T00:00:00PureStandardhttp://www.xbrl.org/2003/instancepurexbrli0USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2false falsefalseD2012_ObligationsUnderLloydsCentralFundMemberhttp://www.sec.gov/CIK0001165880duration2012-01-01T00:00:002012-12-31T00:00:00PureStandardhttp://www.xbrl.org/2003/instancepurexbrli01true 3us-gaap_LossContingenciesLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Contingent liabilities2false 4mrh_NumberOfUnresolvedLegalProceedingsOtherThanTribuneLitigationAndLitigationsInNormalCourseOfBusinessmrh_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalsexbrli:integerItemTypeintegerRepresents the number of unresolved legal proceedings other than Tribune litigation and legal proceedings involving insurance and reinsurance contract dispute in the normal course of business.No definition available.false256Number of unresolved legal proceedings, other than Tribune litigation and proceedings involving insurance and reinsurance contract disputes in the normal course of business3false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse2false truefalseI2013Q2_MaximumMemberhttp://www.sec.gov/CIK0001165880instant2013-06-30T00:00:000001-01-01T00:00:00falsefalseMaximumus-gaap_RangeAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_MaximumMemberus-gaap_RangeAxisexplicitMemberPureStandardhttp://www.xbrl.org/2003/instancepurexbrli0nanafalse0Maximum4true 3us-gaap_LossContingenciesLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Contingent liabilities5false 4mrh_ConcentrationRiskPercentageMaximumBasedOnAggregateInvestmentInSingleEntitymrh_falsenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.100.10falsefalsefalse2falsefalsefalse00falsefalsefalsenum:percentItemTypepureRepresents the maximum percentage of concentration risk arising out of aggregate investments in single investee by the entity. It is expressed as a percentage of the entity's common shareholders' equity.No definition available.false0Percentage of concentration risk, maximum6false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3false USDtruefalse$D2013Q2YTD_ObligationsUnderLloydsCentralFundMemberhttp://www.sec.gov/CIK0001165880duration2013-01-01T00:00:002013-06-30T00:00:00falsefalseLloyd's Central Fund (the "Central Fund")us-gaap_LossContingenciesByNatureOfContingencyAxisxbrldihttp://xbrl.org/2006/xbrldimrh_ObligationsUnderLloydsCentralFundMemberus-gaap_LossContingenciesByNatureOfContingencyAxisexplicitMemberPureStandardhttp://www.xbrl.org/2003/instancepurexbrli0USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Lloyd's Central Fund (the "Central Fund")7true 3us-gaap_LossContingenciesLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Contingent liabilities8false 4mrh_LevyImposedAsPercentageOfPremiumsWrittenmrh_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.0050.005falsefalsefalse2truetruefalse0.0050.005falsefalsefalsenum:percentItemTypepureRepresents the levy imposed on members as a percentage of each members' written premiums to fulfill the funding requirements of the Lloyd's Central Fund (the "Central Fund").No definition available.false0Annual levy imposed on members (as a percent)9false 4mrh_ProbableAdditionalContributionAsPercentageOfUnderwritingCapacityMaximummrh_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.0300.030falsefalsefalse2falsefalsefalse00falsefalsefalsenum:percentItemTypepureRepresents the percentage of additional contribution to the Central Fund which the Council of Lloyd's has the power to impose on members. It is expressed as a percentage of the underwriting capacity of each member in each year.No definition available.false0Percentage of additional contribution to the Central Fund, maximum10false 4mrh_EstimatedObligationToCentralFundForAnnualContributionmrh_falsedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse11000001.1USD$falsetruefalse2falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the entity's estimate of the amount of contribution towards the Central Fund which it might be required to pay.No definition available.false2Estimated obligation to the Central Fund for contribution (in dollars)11false 4mrh_AnnualSubscriptionChargeAsPercentageOfPremiumWrittenmrh_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.0050.005falsefalsefalse2truetruefalse0.0050.005falsefalsefalsenum:percentItemTypepureRepresents the annual subscription charges based on the percentage of premiums written.No definition available.false0Annual subscription charge (as a percent)12false 4mrh_EstimatedObligationForAnnualSubscriptionChargesmrh_falsedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse24000002.4USD$falsetruefalse2falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the entity's estimate of the amount of annual subscription charges towards Lloyd's which it might be required to pay.No definition available.false2Estimated obligation to Lloyd's for annual subscription charges (in dollars)falseCommitments and Contingent Liabilities (Details 2) (USD $)HundredThousandsUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.montpelierre.bm/role/DisclosureCommitmentsAndContingentLiabilitiesDetails2212