Fair Value Measurement - Reconciliation of Beginning and Ending Balances of Recurring Level 3 Fair Value Measurements (Details) - Level 3 $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value, Beginning Balance	$ 108,178
Net Gain	(26,070)	[1]
Fair value, Ending Balance	82,108
Tax Receivable Agreement Liability
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value, Beginning Balance	4,600
Fair value, Ending Balance	4,600
Fathom OpCo Acquisitions Contingent Consideration
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value, Beginning Balance	3,598
Fair value, Ending Balance	3,598
Sponsor Earnout Shares Liability
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value, Beginning Balance	9,380
Net Gain	(2,360)	[1]
Fair value, Ending Balance	7,020
Fathom Earnout Shares Liability
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value, Beginning Balance	64,300
Net Gain	(16,610)	[1]
Fair value, Ending Balance	47,690
Warrant liability – Private Placement Warrants
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value, Beginning Balance	26,300
Net Gain	(7,100)	[1]
Fair value, Ending Balance	$ 19,200

[1] Net gains on changes in recurring level 3 fair value measurements are recognized in Other income in our unaudited consolidated statement of comprehensive loss.