2.4.0.84100 - Disclosure - Commitments and Contingencies (Details)truefalseIn Millions, unless otherwise specifiedfalse1false USDfalsefalse$D2013Q1_M03http://www.sec.gov/CIK0001274792duration2013-03-01T00:00:002013-03-31T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2false USDfalsefalse$I2013Q2http://www.sec.gov/CIK0001274792instant2013-06-30T00:00:000001-01-01T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$1true 2us-gaap_LeasesOperatingAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Operating Leases2false 3mack_OperatingLeasesFutureMinimumPaymentsDueAmendmentmack_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse26000002.6USD$falsetruefalse2falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the amount of required minimum rental payments for leases having an initial or remaining non-cancelable term in excess of one year related to the lease amendment.No definition available.false2Aggregate rent due over amended term of lease3false 3mack_OperatingLeasesAdditionalReimbursementForTenantImprovementsmack_falsedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse6000000.6falsefalsefalse2falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the additional amount of tenant improvements agreed to be reimbursed by landlord under the lease amendment.No definition available.false2Additional reimbursement for tenant improvements agreed by landlord per lease amendment4false 3mack_OperatingLeasesReimbursementForTenantImprovementsOutstandingAmountmack_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2truefalsefalse48000004.8USD$falsetruefalsexbrli:monetaryItemTypemonetaryRepresents the outstanding balance at the end of the period of tenant improvements reimbursable by landlord under the lease agreement.No definition available.false2Aggregate landlord reimbursable tenant improvements outstanding under the existing lease and the lease amendmentfalseCommitments and Contingencies (Details) (USD $)HundredThousandsUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.merrimackpharma.com/role/DisclosureCommitmentsAndContingenciesDetails24