Revenue - Disclosure Of Changes In Trade Receivables Contract Assets And Contract Liabilities Explanatory (Detail) € in Thousands	6 Months Ended
Jun. 30, 2018 EUR (€)
Disclosure of changes in trade receivables, contract assets and contract liabilities [line items]
Trade and other receivables, beginning balance	€ 1,594
Trade and other receivables, additions	12,103
Trade and other receivables, deductions	(11,628)
Trade and other receivables, ending balance	2,069
Contract assets, beginning balance	710
Contract assets, additions	693
Contract assets, deductions	(957)
Contract assets, ending balance	446
Contract liabilities, beginning balance	128,486
Contract liabilities, additions	3,430
Contract liabilities, deductions	(9,226)
Contract liabilities, ending balance	122,690
Deferred revenue [member]
Disclosure of changes in trade receivables, contract assets and contract liabilities [line items]
Contract liabilities, beginning balance	128,486
Contract liabilities, additions	3,430
Contract liabilities, deductions	(9,226)
Contract liabilities, ending balance	122,690
Trade receivables [member]
Disclosure of changes in trade receivables, contract assets and contract liabilities [line items]
Trade and other receivables, beginning balance	1,594
Trade and other receivables, additions	12,103
Trade and other receivables, deductions	(11,628)
Trade and other receivables, ending balance	2,069
Unbilled receivables [member]
Disclosure of changes in trade receivables, contract assets and contract liabilities [line items]
Contract assets, beginning balance	710
Contract assets, additions	693
Contract assets, deductions	(957)
Contract assets, ending balance	€ 446

The amount of an entity’s right to consideration in exchange for goods or services that the entity has transferred to a customer, when that right is conditioned on something other than the passage of time (for example, the entity’s future performance).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 15
-IssueDate 2018-01-01
-Paragraph 105
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_105&doctype=Standard
-URIDate 2018-03-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 15
-IssueDate 2018-01-01
-Paragraph 116
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_116_a&doctype=Standard
-URIDate 2018-03-16

+ Details

Name:	ifrs-full_ContractAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of an entity’s obligation to transfer goods or services to a customer for which the entity has received consideration (or the amount is due) from the customer.

+ References

+ Details

Name:	ifrs-full_ContractLiabilities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of trade receivables and other receivables. [Refer: Trade receivables; Other receivables]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 54
-Subparagraph h
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_54_h&doctype=Standard
-URIDate 2018-03-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 78
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_78_b&doctype=Standard
-URIDate 2018-03-16

+ Details

Name:	ifrs-full_TradeAndOtherReceivables
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Additions in contract assets.

+ References

No definition available.

+ Details

Name:	mrus_AdditionsInContractAssets
Namespace Prefix:	mrus_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Additions in contract liabilities.

+ References

No definition available.

+ Details

Name:	mrus_AdditionsInContractLiabilities
Namespace Prefix:	mrus_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Additions to trade and other receivables.

+ References

No definition available.

+ Details

Name:	mrus_AdditionsToTradeAndOtherReceivables
Namespace Prefix:	mrus_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Deductions in contract assets.

+ References

No definition available.

+ Details

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

- Definition

Deductions in contract liabilities.

+ References

No definition available.

+ Details

Name:	mrus_DeductionsInContractLiabilities
Namespace Prefix:	mrus_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Deductions in trade and other receivables.

+ References

No definition available.

+ Details

Name:	mrus_DeductionsInTradeAndOtherReceivables
Namespace Prefix:	mrus_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Disclosure of changes in trade receivables, contract assets and contract liabilities [line items]

+ References

No definition available.

+ Details

Name:	mrus_DisclosureOfChangesInTradeReceivablesContractAssetsAndContractLiabilitiesLineItems
Namespace Prefix:	mrus_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	ifrs-full_ClassesOfLiabilitiesAxis=mrus_DeferredRevenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfAssetsAxis=ifrs-full_TradeReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfAssetsAxis=mrus_UnbilledReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: