Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8672-108599

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Segment Reporting - Narrative (Details)	9 Months Ended
Segment Reporting - Narrative (Details)	Sep. 30, 2021 clinic segment	Jun. 30, 2021 clinic	Dec. 31, 2020 clinic	Sep. 30, 2020 clinic	Jun. 30, 2020 clinic	Dec. 31, 2019 clinic
Segment Reporting Information [Line Items]
Number of operating segments \| segment	2
Number of non-operating segments \| segment	1
Number of Stores	666			560
Company-Owned or Managed Clinics
Segment Reporting Information [Line Items]
Number of Stores	83	78	64	63	62	60
Franchised Clinics
Segment Reporting Information [Line Items]
Number of Stores	583	555	515	497	477	453