Goodwill and Intangible Assets - Aggregate amortization expense - Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
TOI Parent Inc.
Finite-Lived Intangible Assets [Line Items]
Total segment amortization	$ 625,189	$ 612,689	$ 1,858,902	$ 1,874,390	$ 2,487,078	$ 2,523,400	$ 707,954

The aggregate amount of recurring noncash expense charged against earnings in the period to allocate the cost of assets over their estimated remaining economic lives.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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