Quarterly report pursuant to Section 13 or 15(d)

Revenue Recognition - Disaggregation of Revenue (Details)

v3.23.2
Revenue Recognition - Disaggregation of Revenue (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jun. 30, 2023
Jun. 30, 2022
Jun. 30, 2023
Jun. 30, 2022
Disaggregation of Revenue [Line Items]        
Revenue $ 1,188,677 $ 1,125,785 $ 3,644,775 $ 3,453,987
U.S. federal government agencies        
Disaggregation of Revenue [Line Items]        
Revenue $ 568,924 $ 507,047 $ 1,742,739 $ 1,624,848
U.S. federal government agencies | Revenue Benchmark | Customer Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 47.90% 45.00% 47.80% 47.00%
U.S. state government agencies        
Disaggregation of Revenue [Line Items]        
Revenue $ 445,855 $ 401,042 $ 1,329,766 $ 1,183,876
U.S. state government agencies | Revenue Benchmark | Customer Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 37.50% 35.70% 36.50% 34.30%
International government agencies        
Disaggregation of Revenue [Line Items]        
Revenue $ 148,742 $ 191,753 $ 491,861 $ 557,928
International government agencies | Revenue Benchmark | Customer Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 12.50% 17.00% 13.50% 16.20%
Other, including local municipalities and commercial customers        
Disaggregation of Revenue [Line Items]        
Revenue $ 25,156 $ 25,943 $ 80,409 $ 87,335
Other, including local municipalities and commercial customers | Revenue Benchmark | Customer Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 2.10% 2.30% 2.20% 2.50%
Performance-based        
Disaggregation of Revenue [Line Items]        
Revenue $ 617,800 $ 520,202 $ 1,761,764 $ 1,527,368
Performance-based | Revenue Benchmark | Contract Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 52.00% 46.20% 48.30% 44.20%
Cost-plus        
Disaggregation of Revenue [Line Items]        
Revenue $ 281,014 $ 282,578 $ 940,509 $ 945,482
Cost-plus | Revenue Benchmark | Contract Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 23.60% 25.10% 25.80% 27.40%
Fixed price        
Disaggregation of Revenue [Line Items]        
Revenue $ 171,809 $ 160,219 $ 527,556 $ 470,591
Fixed price | Revenue Benchmark | Contract Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 14.50% 14.20% 14.50% 13.60%
Time and materials        
Disaggregation of Revenue [Line Items]        
Revenue $ 118,054 $ 162,786 $ 414,946 $ 510,546
Time and materials | Revenue Benchmark | Contract Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 9.90% 14.50% 11.40% 14.80%