Quarterly report pursuant to Section 13 or 15(d)

Revenue Recognition - Disaggregation of Revenue (Details)

v3.24.0.1
Revenue Recognition - Disaggregation of Revenue (Details) - USD ($)
$ in Thousands
 3 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Disaggregation of Revenue [Line Items]    
Revenue $ 1,327,041 $ 1,249,246
U. S. federal government agencies    
Disaggregation of Revenue [Line Items]    
Revenue $ 662,946 $ 603,918
U. S. federal government agencies | Revenue Benchmark | Customer Concentration Risk    
Disaggregation of Revenue [Line Items]    
Revenue in % 50.00% 48.30%
U.S. state government agencies    
Disaggregation of Revenue [Line Items]    
Revenue $ 486,943 $ 437,362
U.S. state government agencies | Revenue Benchmark | Customer Concentration Risk    
Disaggregation of Revenue [Line Items]    
Revenue in % 36.70% 35.00%
International government agencies    
Disaggregation of Revenue [Line Items]    
Revenue $ 155,612 $ 181,760
International government agencies | Revenue Benchmark | Customer Concentration Risk    
Disaggregation of Revenue [Line Items]    
Revenue in % 11.70% 14.50%
Other, including local municipalities and commercial customers    
Disaggregation of Revenue [Line Items]    
Revenue $ 21,540 $ 26,206
Other, including local municipalities and commercial customers | Revenue Benchmark | Customer Concentration Risk    
Disaggregation of Revenue [Line Items]    
Revenue in % 1.60% 2.10%
Performance-based    
Disaggregation of Revenue [Line Items]    
Revenue $ 704,711 $ 569,217
Performance-based | Revenue Benchmark | Contract Concentration Risk    
Disaggregation of Revenue [Line Items]    
Revenue in % 53.10% 45.60%
Cost-plus    
Disaggregation of Revenue [Line Items]    
Revenue $ 342,015 $ 347,319
Cost-plus | Revenue Benchmark | Contract Concentration Risk    
Disaggregation of Revenue [Line Items]    
Revenue in % 25.80% 27.80%
Fixed price    
Disaggregation of Revenue [Line Items]    
Revenue $ 176,677 $ 175,073
Fixed price | Revenue Benchmark | Contract Concentration Risk    
Disaggregation of Revenue [Line Items]    
Revenue in % 13.30% 14.00%
Time and materials    
Disaggregation of Revenue [Line Items]    
Revenue $ 103,638 $ 157,637
Time and materials | Revenue Benchmark | Contract Concentration Risk    
Disaggregation of Revenue [Line Items]    
Revenue in % 7.80% 12.60%