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

Amount of expense related to royalty payments under a contractual arrangement such as payment for mineral and drilling rights and use of technology or intellectual property.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.3)
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

Name:	us-gaap_RoyaltyExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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 from fifth anniversary under collaborative arrangement.

No definition available.

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

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

No definition available.

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

Represents the clinical milestone payments potentially due under collaborative arrangement.

No definition available.

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

Amount paid during the period for milestones under collaborative arrangement.

No definition available.

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

Represents the regulatory milestone payments potentially due under collaborative arrangement.

No definition available.

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

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

No definition available.

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

Number of new stock issued to the strategic partner during the period.

No definition available.