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

X

- 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

X

- 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