Loss Per Share - Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Numerator
Net loss	$ (13,563)	$ (14,870)
Less: Net loss attributable to noncontrolling interests	(10,371)	(11,766)
Net loss attributable to Viant Technology Inc.	$ (3,192)	$ (3,104)
Weighted-average shares of Class A common stock outstanding:
Basic	$ (0.23)	$ (0.27)
Diluted	$ (0.23)	$ (0.27)
Anti-dilutive shares excluded from loss per share of Class A common stock—diluted:
Total shares excluded from loss per share of Class A common stock—diluted	55,711	53,632
Class A Common Stock
Weighted-average shares of Class A common stock outstanding:
Weighted-average shares of Class A common stock outstanding—basic and diluted	13,809	11,500
Class B Common Stock
Anti-dilutive shares excluded from loss per share of Class A common stock—diluted:
Total shares excluded from loss per share of Class A common stock—diluted	47,082	47,436
Restricted Stock Units
Anti-dilutive shares excluded from loss per share of Class A common stock—diluted:
Total shares excluded from loss per share of Class A common stock—diluted	4,858	6,196
Nonqualified Stock Options
Anti-dilutive shares excluded from loss per share of Class A common stock—diluted:
Total shares excluded from loss per share of Class A common stock—diluted	3,771