2.4.0.84110 - Disclosure - Subsequent Events (Details)truefalseIn Millions, except Share data, unless otherwise specifiedfalse1false USDfalsefalse$D2013Q3_M0717_SubsequentEventMemberhttp://www.sec.gov/CIK0001274792duration2013-07-16T00:00:002013-07-17T00:00:00SharesStandardhttp://www.xbrl.org/2003/instancesharesxbrli0USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDPerShareDividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0USDUSD$1true 3us-gaap_SubsequentEventLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Subsequent event2false 4us-gaap_StockIssuedDuringPeriodSharesNewIssuesus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalsepositiveLabel1truefalsefalse57500005750000falsefalsefalsexbrli:sharesItemTypesharesNumber of new stock issued during the period.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 false1Shares of common stock sold in underwritten public offering3false 4us-gaap_SharePriceus-gaap_truenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse5.005.00USD$falsetruefalsenum:perShareItemTypedecimalPrice of a single share of a number of saleable stocks of a company.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 false3Public offering price (in dollars per share)4false 4mack_ProceedsFromIssuancePublicEquityAndConvertibleSeniorNotesOfferingNetOfOfferingCostsmack_falsedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse147400000147.4USD$falsetruefalsexbrli:monetaryItemTypemonetaryThe cash inflow associated with the amount received from the entity's sale of common stock and convertible senior notes, net of offering costs.No definition available.false2Net proceeds from sale of common stock and convertible senior notes5false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2false USDtruefalse$D2013Q3_M0717_ConvertibleDebtMember_SubsequentEventMemberhttp://www.sec.gov/CIK0001274792duration2013-07-16T00:00:002013-07-17T00:00:00falsefalseConvertible senior notesus-gaap_DebtInstrumentAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_ConvertibleDebtMemberus-gaap_DebtInstrumentAxisexplicitMemberfalsefalseSubsequent eventsus-gaap_SubsequentEventTypeAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_SubsequentEventMemberus-gaap_SubsequentEventTypeAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170PureStandardhttp://www.xbrl.org/2003/instancepurexbrli0USDUSD$nanafalse0Convertible senior notes6true 3us-gaap_SubsequentEventLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Subsequent event7false 4us-gaap_DebtInstrumentIncreaseAdditionalBorrowingsus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsepositiveLabel1truefalsefalse125000000125.0USD$falsefalsefalsexbrli:monetaryItemTypemonetaryIncrease of additional borrowings on existing and new debt instruments.Reference 1: 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.(f)) -URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph f -Article 4 false2Convertible senior notes issued8false 4us-gaap_DebtInstrumentInterestRateStatedPercentageus-gaap_truenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truetruefalse0.04500.0450falsefalsefalsenum:percentItemTypepureInterest rate stated in the contractual debt agreement.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 false0Interest rate (as a percent)9false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse3false truefalseD2013Q3_M0717_SecuredDebtMember_SubsequentEventMemberhttp://www.sec.gov/CIK0001274792duration2013-07-16T00:00:002013-07-17T00:00:00falsefalseLoan and security agreementus-gaap_DebtInstrumentAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_SecuredDebtMemberus-gaap_DebtInstrumentAxisexplicitMemberfalsefalseSubsequent eventsus-gaap_SubsequentEventTypeAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_SubsequentEventMemberus-gaap_SubsequentEventTypeAxisexplicitMembernanafalse0Loan and security agreement10true 3us-gaap_SubsequentEventLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Subsequent event11false 4mack_DebtInstrumentInterestOnlyPaymentPeriodExtensionmack_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1falsefalsefalse006 monthsfalsefalsefalsexbrli:durationItemTypenaRepresents the extension period for interest only payments as provided under the loan agreement.No definition available.false0Extension period for interest-only payments12false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse4false USDtruefalse$D2013Q3_M0717_SecuredDebtMember_MinimumMember_SubsequentEventMemberhttp://www.sec.gov/CIK0001274792duration2013-07-16T00:00:002013-07-17T00:00:00falsefalseLoan and security agreementus-gaap_DebtInstrumentAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_SecuredDebtMemberus-gaap_DebtInstrumentAxisexplicitMemberfalsefalseSubsequent eventsus-gaap_SubsequentEventTypeAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_SubsequentEventMemberus-gaap_SubsequentEventTypeAxisexplicitMemberfalsefalseMinimumus-gaap_RangeAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_MinimumMemberus-gaap_RangeAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$nanafalse0Loan and security agreement | Minimum13true 3us-gaap_SubsequentEventLineItemsus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Subsequent event14false 4mack_DebtInstrumentGrossProceedsInOneOrMoreTransactionsPriorToSpecifiedDatemack_falsedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse7500000075USD$falsetruefalsexbrli:monetaryItemTypemonetaryRepresents the amount of gross proceeds in one or more transactions prior to December 1, 2013 that the Company may elect to extend the interest-only period by six months so that the aggregate outstanding principal balance of the loan would be repaid in monthly installments starting on June 1, 2014 and continuing through November 1, 2016.No definition available.false2Amount of gross proceeds in one or more transactions prior to December 1, 2013 that the Company may elect to extend the interest-only period by six monthsfalseSubsequent Events (Details) (Subsequent events, USD $)HundredThousandsNoRoundingNoRoundingUnKnowntruefalsefalseSheethttp://www.merrimackpharma.com/role/DisclosureSubsequentEventsDetails114