Noncontrolling Interests - Summary of Effect of Changes in Ownership Interest in Viant Technology LLC on Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Noncontrolling Interest [Abstract]
Net loss attributable to Viant Technology Inc.	$ (3,401)	$ (3,655)	$ (6,593)	$ (6,760)
Transfers to noncontrolling interests:
Decrease in the additional-paid-in-capital of Viant Technology Inc. resulting from ownership changes in Viant Technology LLC	(5,455)		(9,731)
Net decrease in equity of Viant Technology Inc. due to equity interest transactions with noncontrolling interests	$ (8,856)		$ (16,324)