Annual report pursuant to Section 13 and 15(d)

Business and summary of significant accounting policies - Narrative (Details)

v3.20.2
Business and summary of significant accounting policies - Narrative (Details)
 3 Months Ended 12 Months Ended
Jul. 01, 2020
USD ($)
Mar. 31, 2020
USD ($)
$ / shares
Sep. 30, 2020
USD ($)
segment
Sep. 30, 2019
USD ($)
Sep. 30, 2018
USD ($)
Oct. 01, 2019
USD ($)
Property and Equipment            
Goodwill     $ 593,129,000 $ 584,469,000 $ 399,882,000  
Number of business segments | segment     3      
Accounts receivable     $ 786,200,000      
Bad debt expense     2,800,000      
Revenue adjustment   $ 24,000,000        
Earnings per share adjustment (in dollars per share) | $ / shares   $ 0.28        
Net income adjustment   $ 18,000,000        
Total lease liabilities     184,759,000      
Goodwill, impairment loss $ 0          
Impairment of long-lived assets held-for-use         0  
Accounting Standards Update 2016-02            
Property and Equipment            
Total lease liabilities           $ 214,500,000
Office space            
Property and Equipment            
Total lease liabilities     $ 171,610,000      
Office space | Maximum            
Property and Equipment            
Estimated useful lives     39 years      
Office furniture and equipment. | Maximum            
Property and Equipment            
Estimated useful lives     7 years      
Software development costs. | Minimum            
Property and Equipment            
Estimated useful lives     3 years      
Software development costs. | Maximum            
Property and Equipment            
Estimated useful lives     8 years      
U.S. Services            
Property and Equipment            
Goodwill     $ 164,472,000 164,472,000 $ 139,588,000  
Impairment of long-lived assets held-for-use     $ 1,200,000 $ 3,700,000