Annual report pursuant to Section 13 and 15(d)

Concentrations of credit risk and major customers Narrative (Details)

v3.10.0.1
Concentrations of credit risk and major customers Narrative (Details) - Total Revenue
12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2016
Foreign Customers      
Concentration Risk [Line Items]      
Percentage of total revenue 29.00% 28.00% 28.00%
U.S. Federal Government      
Concentration Risk [Line Items]      
Percentage of total revenue 16.00% 19.00% 22.00%
United Kingdom      
Concentration Risk [Line Items]      
Percentage of total revenue 12.00% 12.00% 16.00%
New York      
Concentration Risk [Line Items]      
Percentage of total revenue 16.00% 15.00% 12.00%
Australia Government      
Concentration Risk [Line Items]      
Percentage of total revenue 10.00%    
Minimum | U.S. Federal Government      
Concentration Risk [Line Items]      
Percentage of total revenue 10.00%    
Minimum | United Kingdom      
Concentration Risk [Line Items]      
Percentage of total revenue 10.00%    
Minimum | New York      
Concentration Risk [Line Items]      
Percentage of total revenue 10.00%    
Minimum | Australia Government      
Concentration Risk [Line Items]      
Percentage of total revenue 10.00%