Annual report pursuant to Section 13 and 15(d)

Business combinations and disposal Business combinations and disposals - Assessments Australia (Details)

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Business combinations and disposal Business combinations and disposals - Assessments Australia (Details)
$ in Thousands
Dec. 15, 2015
USD ($)
company
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2016
USD ($)
Business Acquisition [Line Items]        
Goodwill   $ 399,882 $ 402,976 $ 397,558
Assessments Australia        
Business Acquisition [Line Items]        
Share capital acquired (as a percent) 100.00%      
Number of businesses acquired | company 3      
Cash consideration $ 2,600      
Contingent consideration, liability, current 500 400    
Intangible assets 400      
Human Services        
Business Acquisition [Line Items]        
Goodwill   $ 44,993 $ 46,368 $ 45,731
Human Services | Assessments Australia        
Business Acquisition [Line Items]        
Goodwill $ 3,000      
Customer relationships | Assessments Australia        
Business Acquisition [Line Items]        
Useful life 6 years