Quarterly report pursuant to Section 13 or 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
 3 Months Ended 9 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Franchisor, Number of Clinics [Roll Forward]        
Clinics in operation at the end of the period 560 488 560 488
Clinic licenses sold but not yet developed 178 179 178 179
Future clinic licenses under executed letters of intent 40 29 40 29
Franchised clinics        
Franchisor, Number of Clinics [Roll Forward]        
Clinics open at beginning of period 477 417 453 394
Opened during the period 21 21 49 47
Sold during the period 0 (6) 0 (7)
Closed during the period (1) (2) (5) (4)
Clinics in operation at the end of the period 497 430 497 430
Company-owned or managed clinics        
Franchisor, Number of Clinics [Roll Forward]        
Clinics open at beginning of period 62 51 60 48
Opened during the period 1 1 3 4
Acquired during the period 0 6 0 7
Closed during the period 0 0 0 (1)
Clinics in operation at the end of the period 63 58 63 58