XML 13 R1.htm IDEA: XBRL DOCUMENT v3.6.0.2
Document and Entity Information Document and Entity Information - USD ($)
$ in Millions
 12 Months Ended
Sep. 30, 2016
Dec. 13, 2016
Mar. 31, 2016
Document Information [Line Items]      
Entity Registrant Name RMR Group Inc.    
Entity Central Index Key 0001644378    
Document Type 10-K    
Document Period End Date Sep. 30, 2016    
Amendment Flag false    
Current Fiscal Year End Date --09-30    
Entity Current Reporting Status Yes    
Entity Filer Category Non-accelerated Filer    
Document Fiscal Year Focus 2016    
Document Fiscal Period Focus FY    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Public Float     $ 173.2
Class A common shares      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   15,082,432  
Class B-1 common shares      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   1,000,000  
Class B-2 common shares      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   15,000,000