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Earnings Per Share - Additional Information (Detail) | Sep. 30, 2021 Class
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Earnings Per Shares [Abstract] |
Number of classes of common stock | 2

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- Definition The number of classes of common stock of the entity. + References No definition available. + Details
Name: | ttd_CommonStockNumberOfClasses
Namespace Prefix: | ttd_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Earnings Per Shares [Abstract] + References No definition available. + Details
Name: | ttd_EarningsPerSharesAbstract
Namespace Prefix: | ttd_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration