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

Carrying value as of the balance sheet date of obligations incurred through that date and payable for milestone payments.

No definition available.

Name:	ymab_AccruedMilestonePayments
Namespace Prefix:	ymab_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Carrying value as of the balance sheet date of obligations incurred through that date and payable for milestone payments. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

No definition available.

Name:	ymab_AccruedMilestonePaymentsCurrent
Namespace Prefix:	ymab_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Carrying value as of the balance sheet date of obligations incurred through that date and due after one year (or beyond the operating cycle if longer) for milestone payments.

No definition available.

Name:	ymab_AccruedMilestonePaymentsNoncurrent
Namespace Prefix:	ymab_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the annual minimum royalties payable under arrangement other than collaborative.

No definition available.

Name:	ymab_ArrangementOtherThanCollaborativeAnnualMinimumRoyaltiesPayable
Namespace Prefix:	ymab_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the annual minimum royalties payable from tenth anniversary under arrangement other than collaborative.

No definition available.

Name:	ymab_ArrangementOtherThanCollaborativeAnnualMinimumRoyaltiesPayableFromTenthAnniversary
Namespace Prefix:	ymab_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount charged for clinical milestone expense during the period under arrangement other than collaborative.

No definition available.

Name:	ymab_ArrangementOtherThanCollaborativeClinicalMilestoneExpense
Namespace Prefix:	ymab_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount paid during the period for clinical milestones under arrangement other than collaborative.

No definition available.

Name:	ymab_ArrangementOtherThanCollaborativeClinicalMilestonePayment
Namespace Prefix:	ymab_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the clinical milestone payments potentially due under arrangement other than collaborations.

No definition available.

Name:	ymab_ArrangementOtherThanCollaborativeClinicalMilestonePaymentsDue
Namespace Prefix:	ymab_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the regulatory milestone payments potentially due under arrangement other than collaborative.

No definition available.

Name:	ymab_ArrangementOtherThanCollaborativeRegulatoryMilestonePaymentsDue
Namespace Prefix:	ymab_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the sales based milestones payments potentially due under arrangement other than collaborative.

No definition available.