Noncontrolling Interests - Summary Ownership of Viant Technology LLC (Details) - Viant Technology LLC - shares	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Minority Interest [Line Items]
Units Owned	61,153,742	60,811,768
Ownership Percentage	100.00%	100.00%
Viant Technology Inc.
Minority Interest [Line Items]
Units Owned	14,071,482	13,704,638
Ownership percentage by Viant Technology Inc.	23.00%	22.50%
Non-controlling Interest
Minority Interest [Line Items]
Units Owned	47,082,260	47,107,130
Ownership percentage by non-controlling interests	77.00%	77.50%