Additional loan advances upon occurrence of certain funding conditions.

No definition available.

Name:	mack_AdditionalLoanAdvancesUponOccurrenceOfCertainFundingConditions
Namespace Prefix:	mack_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Debt instrument repayment fee percentage.

+ References

No definition available.

+ Details

Name:	mack_DebtInstrumentRepaymentFeePercentage
Namespace Prefix:	mack_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the maximum cumulative amount of milestone payments that can be received over the life of the license and collaboration agreements.

+ References

No definition available.

+ Details

Name:	mack_MaximumCollaborativeArrangementMilestonePayments
Namespace Prefix:	mack_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Potential milestone payments receivable.

+ References

No definition available.

+ Details

Name:	mack_PotentialMilestonePaymentsReceivable
Namespace Prefix:	mack_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of the fee that accompanies borrowing money under the debt instrument.

+ References

+ Details

Name:	us-gaap_DebtInstrumentFeeAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateTerms
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of the payment terms of the debt instrument (for example, whether periodic payments include principal and frequency of payments) and discussion about any contingencies associated with the payment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentPaymentTerms
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

End date of debt instrument redemption period, in CCYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Start date of debt instrument redemption period, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_DebtInstrumentRedemptionPeriodStartDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of consideration recognized during the period for the milestone or milestones.

+ References

No definition available.

+ Details

Name:	us-gaap_RevenueRecognitionMilestoneMethodRevenueRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Details

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- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Period Type:

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Balance Type:
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- Details

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- Details

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Balance Type:
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- Details

Name:	us-gaap_LongtermDebtTypeAxis=mack_TermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Balance Type:
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- Details

Name:	us-gaap_StatementScenarioAxis=mack_PriotToDecemberThreeOneTwoZeroOneNineMember
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- Details

Name:	us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix:
Data Type:	na
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Subsequent Events - Additional Information (Detail) - USD ($)				1 Months Ended
	Aug. 07, 2018	Jul. 02, 2018	Apr. 03, 2017	Aug. 31, 2018
Ipsen [Member] \| Asset Sale Agreement [Member] \| Development And Commercialization Milestones
Subsequent Event [Line Items]
Maximum amount of milestone payments that can be received			$ 33,000,000
Ipsen [Member] \| Asset Sale Agreement [Member] \| Sale Milestone In Major European Countries
Subsequent Event [Line Items]
Potential milestone payments receivable			18,000,000
Ipsen [Member] \| Asset Sale Agreement [Member] \| Sale Milestone In Major Non European And Non Asian Country
Subsequent Event [Line Items]
Potential milestone payments receivable			5,000,000
Ipsen [Member] \| Asset Sale Agreement [Member] \| Clinical Trials In Lung Cancer
Subsequent Event [Line Items]
Potential milestone payments receivable			$ 10,000,000
Scenario Forecast [Member]
Subsequent Event [Line Items]
Milestone payment received				$ 18,000,000
Scenario Forecast [Member] \| Asset Sale Agreement [Member] \| Sale Milestone In Major European Countries
Subsequent Event [Line Items]
Milestone payment received				$ 18,000,000
Subsequent Event [Member] \| Baxalta \| Asset Sale Agreement [Member] \| Development And Commercialization Milestones
Subsequent Event [Line Items]
Milestone payment received	$ 18,000,000
Subsequent Event [Member] \| Term Loan [Member] \| Loan Agreement [Member] \| Hercules Capital, Inc [Member]
Subsequent Event [Line Items]
Aggregate principal amount of loan		$ 25,000,000
Debt instrument, initial advance received		$ 15,000,000
Debt instrument, interest rate terms		The term loan bears interest at an annual rate equal to the greater of 9.25% and 9.25% plus the prime rate of interest minus 5.25%.
Debt instrument, interest rate percentage		9.25%
Debt instrument, term		18 months
Outstanding principal balance repayment start date		Feb. 01, 2020
Outstanding principal balance repayment end date		Aug. 01, 2021
Debt instruement, payment terms		The Loan Agreement provides for interest-only payments for eighteen months and repayment of the aggregate outstanding principal balance of the term loan in monthly installments starting on February 1, 2020 and continuing through August 1, 2021.
Payment of debt instrument fee amount		$ 250,000
Debt instrument, repayment fee percentage		5.55%
Subsequent Event [Member] \| Term Loan [Member] \| Loan Agreement [Member] \| Hercules Capital, Inc [Member] \| Prior To December 31, 2018 [Member]
Subsequent Event [Line Items]
Debt instrument, initial advance amount		$ 5,000,000
Subsequent Event [Member] \| Term Loan [Member] \| Loan Agreement [Member] \| Hercules Capital, Inc [Member] \| Prior To December 31, 2019 [Member]
Subsequent Event [Line Items]
Debt instrument, initial advance amount		$ 5,000,000
Subsequent Event [Member] \| Term Loan [Member] \| Loan Agreement [Member] \| Hercules Capital, Inc [Member] \| Prime Rate [Member]
Subsequent Event [Line Items]
Debt instrument, percentage deducted from interest rate and prime rate		5.25%