Annual report pursuant to Section 13 and 15(d)

Business and summary of significant accounting policies - Revenue Recognition (Details)

v3.10.0.1
Business and summary of significant accounting policies - Revenue Recognition (Details) - Total Revenue
12 Months Ended
Sep. 30, 2018
Performance-based contracts  
Concentration Risk [Line Items]  
Percentage of total revenue 43.00%
Cost-plus contracts  
Concentration Risk [Line Items]  
Percentage of total revenue 33.00%
Fixed-price contracts  
Concentration Risk [Line Items]  
Percentage of total revenue 18.00%
Time and materials contracts  
Concentration Risk [Line Items]  
Percentage of total revenue 6.00%