Stockholders' Equity (Deficit) - Convertible Preferred Stock (Details)	Jun. 07, 2019 shares
Private Oncternal
Class Of Stock [Line Items]
Convertible preferred stock converted into common stock shares	8,148,268

Number of shares issued for each share of convertible preferred stock that is converted.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section S99
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Name:	us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant