Annual report pursuant to Section 13 and 15(d)

Concentrations of credit risk and major customers - Schedule of Concentration of Risk, by Risk Factor (Details)

v3.5.0.2
Concentrations of credit risk and major customers - Schedule of Concentration of Risk, by Risk Factor (Details) - Total Revenue
12 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2014
U.S. Federal      
Revenue Recognition      
Revenue from major customers (as a percent) 22.00% 20.00% 17.00%
United Kingdom Government      
Revenue Recognition      
Revenue from major customers (as a percent) 16.00%    
State of New York      
Revenue Recognition      
Revenue from major customers (as a percent) 12.00% 10.00%  
Australia      
Revenue Recognition      
Revenue from major customers (as a percent)     10.00%
State of California      
Revenue Recognition      
Revenue from major customers (as a percent)     10.00%
State of Texas      
Revenue Recognition      
Revenue from major customers (as a percent)     10.00%
Maximum | United Kingdom Government      
Revenue Recognition      
Revenue from major customers (as a percent)   10.00% 10.00%
Maximum | State of New York      
Revenue Recognition      
Revenue from major customers (as a percent)     10.00%
Maximum | Australia      
Revenue Recognition      
Revenue from major customers (as a percent) 10.00%    
Maximum | State of California      
Revenue Recognition      
Revenue from major customers (as a percent) 10.00%   10.00%
Maximum | State of Texas      
Revenue Recognition      
Revenue from major customers (as a percent) 10.00%