Term of initially exercisable warrants or rights outstanding.

No definition available.

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

- Definition

Number of warrants or rights issued during the period.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Common stock volume weighted average price threshold for redeeming a class of right or warrant.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

The period after which the warrants or rights can redeemed at a stated redemption price.

+ References

No definition available.

+ Details

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

- Definition

The redemption price of warrant or right at which it is redeemed after the redemption period.

+ References

No definition available.

+ Details

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Namespace Prefix:	ontx_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Threshold period of specified consecutive trading days during which the volume weighted average price of stock is above a particular price.

+ References

No definition available.

+ Details

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

- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(i)(4))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Number of securities into which each warrant or right may be converted. For example, but not limited to, each warrant may be converted into two shares.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Number of new stock issued during the period.

+ References

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(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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-Name Accounting Standards Codification
-Topic 210
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
Data Type:	na
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Period Type:

- Details

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Fair Value Measurements - Rights Offering (Details) - Dealer-Manager Agreement, rights offering - $ / shares	May 01, 2018	Feb. 12, 2018	Jul. 29, 2016
Sale of Securities
Issuance of stock (in shares)	3,694,118	467,000	239,986
Tradable warrants
Sale of Securities
Rights or warrants issued (in shares)			212,801
Exercisable, term (in years)			5 years
Shares into which each warrant can be converted (in shares)			1
Exercise price (in dollars per share)			$ 73.80
Redemption period (in years)			1 year
Redemption price (in dollars per share)			$ 0.001
Volume weighted average price per share of common stock (in dollars per share)			$ 184.50
Threshold consecutive trading days (in days)			10 days
Pre-funded warrants
Sale of Securities
Rights or warrants issued (in shares)			43,760