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[Axis] Preferred stock shares issued Preferred Stock, Shares Issued Entity Small Business Entity Small Business Leases Lessee, Operating Lease, Liability, Payment, Due [Abstract] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Sale of stock, number of shares issued in transaction Sale of Stock, Number of Shares Issued in Transaction Silicon Valley Bank Silicon Valley Bank [Member] Silicon Valley Bank Loan and Security Agreement Debt Disclosure [Text Block] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Weighted average remaining contractual term vested (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Proceeds from issuance of common stock for employee stock purchase plan Proceeds from Issuance of Common Stock Amendment Flag Amendment Flag Total future minimum commitments, net Operating Leases, 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[Member] Options to purchase common stock (in shares) Incremental Common Shares Attributable to Dilutive Effect of Call Options Incremental Common Shares Attributable to Dilutive Effect of Call Options Document Quarterly Report Document Quarterly Report Options canceled (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period General and administrative General and Administrative Expense [Member] Equity [Abstract] Total Financial Assets Assets, Fair Value Disclosure EMEA EMEA [Member] Percentage of outstanding stock maximum Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Outstanding Stock Maximum Subsequent Event [Line Items] Subsequent Event [Line Items] Payable to publishers Accounts Payable, Trade, Current Options granted (in usd per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price 2021 (for remaining 3 months) 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marketing Selling and Marketing Expense Property and equipment included in accounts payable and accrued expenses Property And Equipment Included In Accounts Payable And Accrued Expenses Property And Equipment Included In Accounts Payable And Accrued Expenses Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Revenues from External Customers and Long-Lived Assets [Line Items] Revenues from External Customers and Long-Lived Assets [Line Items] Stock-based compensation Total stock-based compensation Share-based Payment Arrangement, Expense Depreciation and amortization Other Depreciation and Amortization Issuance of common stock related to employee stock purchase plan Stock Issued During Period, Value, Employee Stock Purchase Plan Common stock, par value $0.0001 per share; 1,000,000,000 Class A shares authorized as of September 30, 2021 and December 31, 2020; 27,436,489 and 6,801,368 shares issued and outstanding as of September 30, 2021 and 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