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CONVERTIBLE PREFERRED STOCK - Narrative (Details) | Jun. 30, 2021 USD ($)
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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 + References No definition available. + Details
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Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Threshold Proceeds from a Public Offering to Trigger Mandatory Conversion of Convertible Preferred Stock + References No definition available. + Details
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Namespace Prefix: | duol_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration