3.19.3 html 139 270 1 false 46 0 false 5 false false R1.htm 100000 - Document - Document and Entity Information Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DocumentDocumentAndEntityInformation Document and Entity Information Cover 1 false false R2.htm 100010 - Statement - Condensed Consolidated Balance Sheets Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/StatementCondensedConsolidatedBalanceSheets Condensed Consolidated Balance Sheets Statements 2 false false R3.htm 100020 - Statement - Condensed Consolidated Balance Sheets (Parenthetical) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsParenthetical Condensed Consolidated Balance Sheets (Parenthetical) Statements 3 false false R4.htm 100030 - Statement - Condensed Consolidated Statements of Operations and Comprehensive Loss Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLoss Condensed Consolidated Statements of Operations and Comprehensive Loss Statements 4 false false R5.htm 100040 - Statement - Condensed Consolidated Statements of Stockholders' Equity Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/StatementCondensedConsolidatedStatementsOfStockholdersEquity Condensed Consolidated Statements of Stockholders' Equity Statements 5 false false R6.htm 100050 - Statement - Condensed Consolidated Statements of Cash Flows Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlows Condensed Consolidated Statements of Cash Flows Statements 6 false false R7.htm 100060 - Disclosure - Nature of the Business Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureNatureOfBusiness Nature of the Business Notes 7 false false R8.htm 100070 - Disclosure - Summary of Significant Accounting Policies Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies Summary of Significant Accounting Policies Notes 8 false false R9.htm 100080 - Disclosure - Leases Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureLeases Leases Notes 9 false false R10.htm 100090 - Disclosure - Fair Value of Financial Instruments Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureFairValueOfFinancialInstruments Fair Value of Financial Instruments Notes 10 false false R11.htm 100100 - Disclosure - Marketable Securities and Cash Equivalents Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureMarketableSecuritiesAndCashEquivalents Marketable Securities and Cash Equivalents Notes 11 false false R12.htm 100110 - Disclosure - Notes Payable Notes http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureNotesPayable Notes Payable Notes 12 false false R13.htm 100120 - Disclosure - Accounts Payable, Accrued Expenses and Other Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureAccountsPayableAccruedExpensesAndOther Accounts Payable, Accrued Expenses and Other Notes 13 false false R14.htm 100130 - Disclosure - Stock-Based Compensation Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureStockBasedCompensation Stock-Based Compensation Notes 14 false false R15.htm 100140 - Disclosure - Net Loss Per Common Share Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureNetLossPerCommonShare Net Loss Per Common Share Notes 15 false false R16.htm 100150 - Disclosure - Restructuring Activities Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureRestructuringActivities Restructuring Activities Notes 16 false false R17.htm 100160 - Disclosure - Investment in Silver Creek Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureInvestmentInSilverCreek Investment in Silver Creek Notes 17 false false R18.htm 100170 - Disclosure - 14ner Sales Transaction Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/Disclosure14nerSalesTransaction 14ner Sales Transaction Notes 18 false false R19.htm 100180 - Disclosure - Recent Accounting Pronouncements Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureRecentAccountingPronouncements Recent Accounting Pronouncements Notes 19 false false R20.htm 100190 - Disclosure - Subsequent Events Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureSubsequentEvents Subsequent Events Notes 20 false false R21.htm 100200 - Disclosure - Summary of Significant Accounting Policies (Policies) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies Summary of Significant Accounting Policies (Policies) Policies http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies 21 false false R22.htm 100210 - Disclosure - Summary of Significant Accounting Policies (Tables) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesTables Summary of Significant Accounting Policies (Tables) Tables http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies 22 false false R23.htm 100220 - Disclosure - Fair Value of Financial Instruments (Tables) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsTables Fair Value of Financial Instruments (Tables) Tables http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureFairValueOfFinancialInstruments 23 false false R24.htm 100230 - Disclosure - Marketable Securities and Cash Equivalents (Tables) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureMarketableSecuritiesAndCashEquivalentsTables Marketable Securities and Cash Equivalents (Tables) Tables http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureMarketableSecuritiesAndCashEquivalents 24 false false R25.htm 100240 - Disclosure - Accounts Payable, Accrued Expenses and Other (Tables) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureAccountsPayableAccruedExpensesAndOtherTables Accounts Payable, Accrued Expenses and Other (Tables) Tables http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureAccountsPayableAccruedExpensesAndOther 25 false false R26.htm 100250 - Disclosure - Stock-Based Compensation (Tables) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureStockBasedCompensationTables Stock-Based Compensation (Tables) Tables http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureStockBasedCompensation 26 false false R27.htm 100260 - Disclosure - Net Loss Per Common Share (Tables) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureNetLossPerCommonShareTables Net Loss Per Common Share (Tables) Tables http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureNetLossPerCommonShare 27 false false R28.htm 100270 - Disclosure - Restructuring Activities (Tables) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureRestructuringActivitiesTables Restructuring Activities (Tables) Tables http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureRestructuringActivities 28 false false R29.htm 100280 - Disclosure - Nature of the Business - Additional Information (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureNatureOfBusinessAdditionalInformationDetail Nature of the Business - Additional Information (Detail) Details 29 false false R30.htm 100290 - Disclosure - Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesScheduleOfReconciliationOfCashCashEquivalentsAndRestrictedCashDetail Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) Details 30 false false R31.htm 100300 - Disclosure - Leases - Additional Information (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureLeasesAdditionalInformationDetail Leases - Additional Information (Detail) Details 31 false false R32.htm 100310 - Disclosure - Fair Value of Financial Instruments - Summary of Assets Measured at Fair Value on a Recurring Basis (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsSummaryOfAssetsMeasuredAtFairValueOnRecurringBasisDetail Fair Value of Financial Instruments - Summary of Assets Measured at Fair Value on a Recurring Basis (Detail) Details 32 false false R33.htm 100320 - Disclosure - Fair Value of Financial Instruments - Additional Information (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsAdditionalInformationDetail Fair Value of Financial Instruments - Additional Information (Detail) Details 33 false false R34.htm 100330 - Disclosure - Marketable Securities and Cash Equivalents - Summary of Marketable Securities and Cash Equivalents (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureMarketableSecuritiesAndCashEquivalentsSummaryOfMarketableSecuritiesAndCashEquivalentsDetail Marketable Securities and Cash Equivalents - Summary of Marketable Securities and Cash Equivalents (Detail) Details 34 false false R35.htm 100340 - Disclosure - Notes Payable - Additional Information (Detail) Notes http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureNotesPayableAdditionalInformationDetail Notes Payable - Additional Information (Detail) Details 35 false false R36.htm 100350 - Disclosure - Accounts Payable, Accrued Expenses and Other - Schedule of Accounts Payable, Accrued Expenses and Other (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureAccountsPayableAccruedExpensesAndOtherScheduleOfAccountsPayableAccruedExpensesAndOtherDetail Accounts Payable, Accrued Expenses and Other - Schedule of Accounts Payable, Accrued Expenses and Other (Detail) Details 36 false false R37.htm 100360 - Disclosure - Stock-Based Compensation - Additional Information (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetail Stock-Based Compensation - Additional Information (Detail) Details 37 false false R38.htm 100370 - Disclosure - Stock-Based Compensation - Schedule of Assumptions Used to Calculate Fair Value of Options Granted to Employees (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureStockBasedCompensationScheduleOfAssumptionsUsedToCalculateFairValueOfOptionsGrantedToEmployeesDetail Stock-Based Compensation - Schedule of Assumptions Used to Calculate Fair Value of Options Granted to Employees (Detail) Details 38 false false R39.htm 100380 - Disclosure - Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureStockBasedCompensationScheduleOfRecognizedStockBasedCompensationExpenseDetail Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Detail) Details 39 false false R40.htm 100390 - Disclosure - Net Loss Per Common Share - Additional Information (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureNetLossPerCommonShareAdditionalInformationDetail Net Loss Per Common Share - Additional Information (Detail) Details 40 false false R41.htm 100400 - Disclosure - Net Loss Per Common Share - Schedule of Outstanding Options Excluded from Computation of Diluted Loss Per Share (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureNetLossPerCommonShareScheduleOfOutstandingOptionsExcludedFromComputationOfDilutedLossPerShareDetail Net Loss Per Common Share - Schedule of Outstanding Options Excluded from Computation of Diluted Loss Per Share (Detail) Details 41 false false R42.htm 100410 - Disclosure - Restructuring Activities- Additional Information (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureRestructuringActivitiesAdditionalInformationDetail Restructuring Activities- Additional Information (Detail) Details 42 false false R43.htm 100420 - Disclosure - Restructuring Activities - Summary of Charges Related to Restructuring Activities (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureRestructuringActivitiesSummaryOfChargesRelatedToRestructuringActivitiesDetail Restructuring Activities - Summary of Charges Related to Restructuring Activities (Detail) Details 43 false false R44.htm 100430 - Disclosure - Investment in Silver Creek - Additional Information (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/DisclosureInvestmentInSilverCreekAdditionalInformationDetail Investment in Silver Creek - Additional Information (Detail) Details 44 false false R45.htm 100440 - Disclosure - 14ner Sales Transaction - Additional Information (Detail) Sheet http://www.merrimackpharma.com/20190930/taxonomy/role/Disclosure14nerSalesTransactionAdditionalInformationDetail 14ner Sales Transaction - Additional Information (Detail) Details 45 false false All Reports Book All Reports mack-20190930.xml mack-20190930.xsd mack-20190930_cal.xml mack-20190930_def.xml mack-20190930_lab.xml mack-20190930_pre.xml http://fasb.org/us-gaap/2019-01-31 http://xbrl.sec.gov/dei/2019-01-31 http://fasb.org/srt/2019-01-31 http://xbrl.sec.gov/stpr/2018-01-31 true true