Name:	ontx_OperatingLossCarryforwardsIndefiniteLife
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Percentage of operating loss carryforwards indefinite life Limitation.

No definition available.

Name:	ontx_OperatingLossCarryforwardsIndefiniteLifePercentageOfLimitation
Namespace Prefix:	ontx_
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Period Type:	duration

Amount of operating loss carryforward with expiration from 2022 to 2044, before tax effects, available to reduce future taxable income under enacted tax laws.

No definition available.

Name:	ontx_OperatingLossCarryforwardsWithExpirationFrom2022To2044
Namespace Prefix:	ontx_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319

Name:	us-gaap_OperatingLossCarryforwards
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.