Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Operating Leased Assets [Line Items]
Total rent expense	$ 1.6us-gaap_OperatingLeasesRentExpenseNet	$ 1.5us-gaap_OperatingLeasesRentExpenseNet
Life Sciences Tax Incentive Program 2015 [Member]
Operating Leased Assets [Line Items]
Tax incentive awarded	1.4
State research and development tax credits monetized	$ 1.2
Number of incremental employees pledged to be hired	75
Performance period	5 years

Represents period of performance in order to recognize tax incentive award.

No definition available.

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Namespace Prefix:	mack_
Data Type:	xbrli:durationItemType
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Period Type:	duration

- Definition

Represents amount monetized as a result of state research and development tax credits.

+ References

No definition available.

+ Details

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

- Definition

Represents amount of tax incentive awarded during the period.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of employees to be hired under the incentive program over a specified period of time.

+ References

No definition available.

+ Details

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

- Details

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

- Definition

Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41499-112717

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	duration

- Details

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