Noncontrolling Interests - Summary of Effect of Changes in Ownership Interest in Viant Technology LLC on Equity (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Noncontrolling Interest [Abstract]
Net loss attributable to Viant Technology Inc.	$ (455)	$ (1,190)
Transfers to noncontrolling interests:
Decrease in the additional-paid-in-capital of Viant Technology Inc. resulting from ownership changes in Viant Technology LLC	(160)	(2,945)
Change from net loss attributable to Viant Technology Inc. and transfers to noncontrolling interests	$ (615)	$ (4,135)

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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