Additional loan advances upon occurrence of certain funding conditions.

No definition available.

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

- Definition

Debt instrument prepayment fee

+ References

No definition available.

+ Details

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Namespace Prefix:	mack_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Debt instrument prepayment penalty.

+ References

No definition available.

+ Details

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Namespace Prefix:	mack_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Debt instrument prepayments of debt.

+ References

No definition available.

+ Details

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Namespace Prefix:	mack_
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Balance Type:	credit
Period Type:	instant

- Definition

Number of additional optional term loan advances.

+ References

No definition available.

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Balance Type:	na
Period Type:	duration

- Definition

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

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Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the required periodic payments applied to principal.

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Balance Type:	debit
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- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Balance Type:	credit
Period Type:	duration

- Definition

Amount of the cost of borrowed funds accounted for as interest expense.

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- Definition

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

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Borrowings - Loan Agreement - Additional Information (Detail)		3 Months Ended	12 Months Ended
	Jul. 02, 2018 USD ($) Loan	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Apr. 15, 2019 USD ($)
Debt Instrument [Line Items]
Loss on extinguishment of debt			$ (971,000)
Interest expense			1,528,000	$ 956,000
Loan Agreement [Member]
Debt Instrument [Line Items]
Interest expense			$ 1,500,000	1,000,000
Term Loan [Member] \| Loan Agreement [Member]
Debt Instrument [Line Items]
Number of additional optional term loan advances \| Loan	2
Term Loan [Member] \| Loan Agreement [Member] \| Hercules Capital, Inc [Member]
Debt Instrument [Line Items]
Aggregate principal amount of loan	$ 25,000,000
Debt instrument, initial advance received	15,000,000
Scheduled principle repayments				0
Payoff amount				16,000,000	$ 16,000,000
Prepayment penalty				200,000
Prepayment fee				$ 800,000
Loss on extinguishment of debt		$ 1,000,000
Term Loan [Member] \| Loan Agreement [Member] \| Hercules Capital, Inc [Member] \| Prior To December 31, 2018 [Member]
Debt Instrument [Line Items]
Debt instrument, initial advance amount	5,000,000
Term Loan [Member] \| Loan Agreement [Member] \| Hercules Capital, Inc [Member] \| Prior To December 31, 2019 [Member]
Debt Instrument [Line Items]
Debt instrument, initial advance amount	$ 5,000,000