Annual report pursuant to Section 13 and 15(d)

Nature of Operations and Summary of Significant Accounting Policies - Clinics in Operation Under Franchise Agreements or Company-Owned or Managed (Details)

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Nature of Operations and Summary of Significant Accounting Policies - Clinics in Operation Under Franchise Agreements or Company-Owned or Managed (Details) - clinic
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Product Information, Franchised Clinics, Company-Owned Or Managed Clinics, Activity [Roll Forward]    
Clinics open at beginning of period 513  
Clinics in operation at the end of the period 579 513
Clinic licenses sold but not yet developed 212 170
Executed letters of intent for future clinic licenses 41 34
Franchised Units    
Product Information, Franchised Clinics, Company-Owned Or Managed Clinics, Activity [Roll Forward]    
Clinics open at beginning of period 453 394
Opened during the period 70 71
Sold during the period (1) (8)
Closed during the period (7) (4)
Clinics in operation at the end of the period 515 453
Entity Operated Units    
Product Information, Franchised Clinics, Company-Owned Or Managed Clinics, Activity [Roll Forward]    
Clinics open at beginning of period 60 48
Opened during the period 3 5
Acquired during the period 1 8
Closed during the period 0 (1)
Clinics in operation at the end of the period 64 60