Annual report pursuant to Section 13 and 15(d)

Concentrations of credit risk and major customers (Details)

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Concentrations of credit risk and major customers (Details) - Total Revenue
12 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2013
Foreign customers      
Revenue Recognition      
Revenue from major customers (as a percent) 26.00% 23.00% 25.00%
State government agencies      
Revenue Recognition      
Revenue from major customers (as a percent) 50.00%    
Foreign government agencies      
Revenue Recognition      
Revenue from major customers (as a percent) 22.00%    
U.S.-based federal government agencies      
Revenue Recognition      
Revenue from major customers (as a percent) 20.00%    
Other sources including local municipalities and commercial customers      
Revenue Recognition      
Revenue from major customers (as a percent) 8.00%    
State of Texas      
Revenue Recognition      
Revenue from major customers (as a percent)   10.00% 14.00%
State of Texas | Maximum      
Revenue Recognition      
Revenue from major customers (as a percent) 10.00%    
Australia      
Revenue Recognition      
Revenue from major customers (as a percent)   10.00% 12.00%
Australia | Maximum      
Revenue Recognition      
Revenue from major customers (as a percent) 10.00%    
U.S. Federal      
Revenue Recognition      
Revenue from major customers (as a percent) 20.00% 17.00% 12.00%
State of California      
Revenue Recognition      
Revenue from major customers (as a percent)   10.00%  
State of California | Maximum      
Revenue Recognition      
Revenue from major customers (as a percent) 10.00%   10.00%
State of New York      
Revenue Recognition      
Revenue from major customers (as a percent) 10.00%    
State of New York | Maximum      
Revenue Recognition      
Revenue from major customers (as a percent)   10.00% 10.00%