Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurement - Schedule of Fair Value Measurement of Assets and Liabilities Based on Hierarchy (Detail)

v3.22.2.2
Fair Value Measurement - Schedule of Fair Value Measurement of Assets and Liabilities Based on Hierarchy (Detail) - USD ($)
$ in Thousands
Sep. 30, 2022
Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities $ 24,700 $ 115,778
Tax Receivable Agreement    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities 4,400 4,600
Fathom OpCo Acquisitions Contingent Consideration    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities 700 3,598
Sponsor Earnout Shares Liability    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities 1,790 9,380
Fathom Earnout Shares Liability    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities 11,910 64,300
Warrant Liability - Public Warrants    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities 1,720 7,600
Warrant liability – Private Placement Warrants    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities 4,180 26,300
Level 1    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities 1,720 7,600
Level 1 | Warrant Liability - Public Warrants    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities 1,720 7,600
Level 3    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities 22,980 108,178
Level 3 | Tax Receivable Agreement    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities 4,400 4,600
Level 3 | Fathom OpCo Acquisitions Contingent Consideration    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities   3,598
Level 3 | Sponsor Earnout Shares Liability    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities 1,790 9,380
Level 3 | Fathom Earnout Shares Liability    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities 11,910 64,300
Level 3 | Warrant liability – Private Placement Warrants    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities $ 4,180 $ 26,300