Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details) $ in Millions		12 Months Ended
	Apr. 14, 2020 USD ($)	Dec. 31, 2021 USD ($) Customer Supplier	Dec. 31, 2020 USD ($) Customer Supplier	Dec. 31, 2019 USD ($) Customer	Feb. 28, 2021 USD ($)
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Advertising costs		$ 4.1	$ 1.2	$ 1.0
Share-based compensation arrangement by share-based payment award, initial public offering lock-up period		180 days
Vesting, description		A portion of RSUs granted during the year ended December 31, 2021 to certain employees and board members, pursuant to the 2021 LTIP, vested upon expiration of the 180 day IPO lock-up period during the fiscal year ended December 31, 2021. The remainder of RSUs and nonqualified stock options granted to employees will vest through the applicable vesting dates. RSUs generally vest over a period of four years, contingent upon employment on the vesting date. RSUs awarded to board members upon their appointment will vest on the third anniversary of the grant date and RSUs awarded to board members annually will vest on the first anniversary of the grant date. Nonqualified stock options will generally vest based on 4 years of continuous service and have 10-year contractual terms.
Vesting period		4 years
Nonqualified stock options, contractual terms		10 years
Rent expense		$ 4.4	4.2	$ 4.7
Current portion of deferred rent		$ 0.2	$ 0.4
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]		Other current liabilities	Other current liabilities
Noncurrent portion of deferred rent		$ 0.8	$ 0.5
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Other long-term liabilities	Other long-term liabilities
Tax receivable agreement required to make payments to shareholders realized percentage of tax benefits in event that exchange of units to shares		85.00%
Tax receivable agreement expected remaining tax benefit percentage		15.00%
ASU 2018-15
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]		true
Change in accounting principle, accounting standards update, adoption date		Jan. 01, 2021
Change in accounting principle, accounting standards update, immaterial effect [true false]		true
ASU 2019-12
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]		true
Change in accounting principle, accounting standards update, adoption date		Jan. 01, 2021
Change in accounting principle, accounting standards update, immaterial effect [true false]		true
SOFR
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Tax receivable agreement interest payments accrued basis spread rate		5.00%
Viant Technology LLC
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of interest held		22.50%	22.50%
Credit Concentration Risk | Accounts Receivable
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of customer | Customer		2	1
Credit Concentration Risk | Revenue
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of customer | Customer		0	0	0
Concentration risk, percentage		10.00%	10.00%	10.00%
Credit Concentration Risk | Customer One | Accounts Receivable
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage		13.20%	13.70%
Credit Concentration Risk | Customer Two | Accounts Receivable
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage		12.30%
Supplier Concentration Risk | Accounts Payable and Accrued Liabilities
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of supplier | Supplier		1	3
Supplier Concentration Risk | Accounts Payable and Accrued Liabilities | Supplier One
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage		16.80%	15.50%
Supplier Concentration Risk | Accounts Payable and Accrued Liabilities | Supplier Two
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage			11.50%
Supplier Concentration Risk | Accounts Payable and Accrued Liabilities | Supplier Three
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage			10.90%
Paycheck Protection Program Loan
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Proceeds from Issuance of Long-term Debt	$ 6.0
IPO
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Deferred offering costs capitalized			$ 2.2		$ 4.3