Annual report pursuant to Section 13 and 15(d)

Concentrations of credit risk and major customers Narrative (Details)

v3.8.0.1
Concentrations of credit risk and major customers Narrative (Details) - Total Revenue
12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2015
Foreign Customers      
Concentration Risk [Line Items]      
Percentage of total revenue 28.00% 28.00% 26.00%
State And Local Government Agencies      
Concentration Risk [Line Items]      
Percentage of total revenue 49.00%    
Foreign Government Agencies      
Concentration Risk [Line Items]      
Percentage of total revenue 26.00%    
United States Based Federal Government Agencies      
Concentration Risk [Line Items]      
Percentage of total revenue 19.00%    
Other Customers      
Concentration Risk [Line Items]      
Percentage of total revenue 6.00%    
U.S. Federal Government      
Concentration Risk [Line Items]      
Percentage of total revenue 19.00% 22.00% 20.00%
United Kingdom      
Concentration Risk [Line Items]      
Percentage of total revenue 12.00% 16.00%  
New York      
Concentration Risk [Line Items]      
Percentage of total revenue 15.00% 12.00% 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%