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

Corporate restructuring headcount reduction expected to complete month and year.

+ References

No definition available.

+ Details

Name:	mack_CorporateRestructuringHeadcountReductionExpectedToCompleteMonthAndYear
Namespace Prefix:	mack_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- 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

Number of employees after headcount reduction.

+ References

No definition available.

+ Details

Name:	mack_NumberOfEmployeesAfterHeadCountReduction
Namespace Prefix:	mack_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of occurrence of events that triggers clinical trial termination.

+ References

No definition available.

+ Details

Name:	mack_PercentageOfOccurrenceOfEventsThatTriggersClinicalTrialTermination
Namespace Prefix:	mack_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue recognition, expects to receive remaining milestone payment.

+ References

No definition available.

+ Details

Name:	mack_RevenueRecognitionExpectsToReceiveRemainingMilestonePayment
Namespace Prefix:	mack_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount expected to be recognized in earnings for the specified restructuring cost.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 5.P.4(b)(1))
-URI http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 5.P.4(d))
-URI http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747

+ Details

Name:	us-gaap_RestructuringAndRelatedCostExpectedCost1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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

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

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RestructuringCostAndReserveAxis=us-gaap_OneTimeTerminationBenefitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DeferredRevenueArrangementTypeAxis=mack_SHERLOCClinicalTrialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=mack_PriorToDecemberThreeOneTwoZeroOneEightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=mack_PriotToDecemberThreeOneTwoZeroOneNineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=mack_BaxaltaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=mack_AssetSaleAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DeferredRevenueArrangementTypeAxis=mack_DevelopmentAndCommercializationMilestonesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=mack_IpsenSAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DeferredRevenueArrangementTypeAxis=mack_ClinicalTrialsInLungCancerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Subsequent Events - Additional Information (Detail)				1 Months Ended	3 Months Ended	9 Months Ended
Subsequent Events - Additional Information (Detail)	Nov. 07, 2018 USD ($) Employee	Oct. 19, 2018 USD ($)	Apr. 03, 2017 USD ($)	Oct. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Subsequent Event [Member]
Subsequent Event [Line Items]
Milestone payment received				$ 5,000,000
Number of employees after headcount reduction \| Employee	27
Corporate restructuring headcount reduction expected to complete, month and year	2019-02
Subsequent Event [Member] \| Minimum [Member] \| One-time Employee Termination Benefits [Member]
Subsequent Event [Line Items]
Expenses for one-time termination	$ 1,500,000
Subsequent Event [Member] \| Maximum [Member] \| One-time Employee Termination Benefits [Member]
Subsequent Event [Line Items]
Expenses for one-time termination	$ 1,800,000
Subsequent Event [Member] \| SHERLOC Clinical Trial [Member]
Subsequent Event [Line Items]
Percentage of occurrence of events that triggers clinical trial termination		75.00%
Subsequent Event [Member] \| SHERLOC Clinical Trial [Member] \| Prior To December 31, 2018 [Member]
Subsequent Event [Line Items]
Debt instrument, initial advance amount		$ 5,000,000
Subsequent Event [Member] \| SHERLOC Clinical Trial [Member] \| Prior To December 31, 2019 [Member]
Subsequent Event [Line Items]
Debt instrument, initial advance amount		$ 5,000,000
Baxalta \| Asset Sale Agreement [Member] \| Development And Commercialization Milestones
Subsequent Event [Line Items]
Maximum amount of milestone payments that can be received			$ 33,000,000			$ 33,000,000
Milestone payment received					$ 23,000,000	$ 23,000,000
Baxalta \| Subsequent Event [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
Milestone payment received				28,000,000
Ipsen [Member] \| Subsequent Event [Member] \| Asset Sale Agreement [Member] \| Clinical Trials In Lung Cancer
Subsequent Event [Line Items]
Remaining potential milestone payment receivable				5,000,000
Milestone payment received				$ 5,000,000