Name:	ontx_ConsolidatedOmnibusBudgetReconciliationActCoverageAdditionalNumberOfMonths
Namespace Prefix:	ontx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The period in which the coverage of Consolidated Omnibus Budget Reconciliation Act, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but not limited to, weeks in a year or quarter.

No definition available.

Name:	ontx_ConsolidatedOmnibusBudgetReconciliationActCoverageNumberOfMonths
Namespace Prefix:	ontx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The amount of fee paid for every extra hour after providing 20 hours of service.

No definition available.

Name:	ontx_ConsultingAgreementConsultingFeePerHourForAdditionalHourWorked
Namespace Prefix:	ontx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The number of hours worked for each partial calendar month during the term.

No definition available.

Name:	ontx_ConsultingAgreementConsultingHours
Namespace Prefix:	ontx_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The period of written notice, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but not limited to, weeks in a year or quarter.

No definition available.

Name:	ontx_ConsultingAgreementNoticePeriod
Namespace Prefix:	ontx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The number of months in which the director has agreed for additional service as per Consultation Agreement.

No definition available.

Name:	ontx_ConsultingAgreementPeriodOfService
Namespace Prefix:	ontx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The amount of consulting fee paid as per agreement.

No definition available.

Name:	ontx_ConsultingAgreementServiceFee
Namespace Prefix:	ontx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The amount of base salary included in severance costs.

No definition available.

Name:	ontx_SeveranceCostsBaseSalaryImmediatelyPriorToResigningDate
Namespace Prefix:	ontx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The 55% of amount of base salary included in severance costs.

No definition available.

Name:	ontx_SeveranceCostsSalary55PercentageOfBaseSalary
Namespace Prefix:	ontx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The amount of savings from workforce reduction.

No definition available.

Name:	ontx_TerminationEstimatedSavings
Namespace Prefix:	ontx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The number of positions eliminated during the period as a result of restructuring activities.

No definition available.

Name:	us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminated
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 5.P.3)
-URI http://asc.fasb.org/extlink&oid=115931487&loc=d3e140864-122747

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 5.P.4(b))
-URI http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Name:	us-gaap_SeveranceCosts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

No definition available.

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

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_RestructuringCostAndReserveAxis=us-gaap_OneTimeTerminationBenefitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_TypeOfArrangementAxis=ontx_ConsultingAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_TypeOfArrangementAxis=ontx_SeparationAndReleaseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: