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CONVERTIBLE PREFERRED STOCK - Narrative (Details)	Jun. 30, 2021 USD ($)
Temporary Equity Disclosure [Abstract]
Threshold proceeds from a public offering to trigger mandatory conversion of convertible preferred stock	$ 50,000,000
Threshold percent of preferred stock holders electing to convert to trigger a mandatory conversion of convertible preferred stock	65.00%

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- Definition

Threshold Percent of Preferred Stock Holders Electing to Convert to Trigger Mandatory Conversion of Convertible Preferred Stock

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No definition available.

+ Details

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- Definition

Threshold Proceeds from a Public Offering to Trigger Mandatory Conversion of Convertible Preferred Stock

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No definition available.

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Namespace Prefix:	duol_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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No definition available.

+ Details

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