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

Amount of expenses incurred but not yet paid classified as other, due within one year or the normal operating cycle, if longer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=121566466&loc=d3e6911-107765

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=121566466&loc=d3e7018-107765

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=121566466&loc=d3e6935-107765

Name:	us-gaap_OtherAccruedLiabilitiesCurrent
Namespace Prefix:	us-gaap_
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 clinical costs. 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_AccruedClinicalCostsCurrent
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 compensation and board fees. 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_AccruedCompensationAndBoardFeesCurrent
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 licensing, milestones and royalties. 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_AccruedLicensingMilestoneAndRoyaltyPaymentsCurrent
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 manufacturing costs. 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_AccruedManufacturingCostsCurrent
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 sales reserves. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

No definition available.