Quarterly report pursuant to Section 13 or 15(d)

Revenue Recognition - Disaggregation of Revenue (Details)

v3.23.1
Revenue Recognition - Disaggregation of Revenue (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Mar. 31, 2023
Mar. 31, 2022
Mar. 31, 2023
Mar. 31, 2022
Disaggregation of Revenue [Line Items]        
Revenue $ 1,206,852 $ 1,177,326 $ 2,456,098 $ 2,328,202
U.S. federal government agencies        
Disaggregation of Revenue [Line Items]        
Revenue $ 569,897 $ 553,707 $ 1,173,815 $ 1,117,801
U.S. federal government agencies | Revenue Benchmark | Customer Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 47.20% 47.00% 47.80% 48.00%
U.S. state government agencies        
Disaggregation of Revenue [Line Items]        
Revenue $ 446,549 $ 411,287 $ 883,911 $ 782,834
U.S. state government agencies | Revenue Benchmark | Customer Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 37.00% 34.90% 36.00% 33.70%
International government agencies        
Disaggregation of Revenue [Line Items]        
Revenue $ 161,359 $ 194,800 $ 343,119 $ 366,175
International government agencies | Revenue Benchmark | Customer Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 13.40% 16.50% 14.00% 15.70%
Other, including local municipalities and commercial customers        
Disaggregation of Revenue [Line Items]        
Revenue $ 29,047 $ 17,532 $ 55,253 $ 61,392
Other, including local municipalities and commercial customers | Revenue Benchmark | Customer Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 2.40% 1.50% 2.20% 2.60%
Performance-based        
Disaggregation of Revenue [Line Items]        
Revenue $ 574,747 $ 516,210 $ 1,143,964 $ 1,007,166
Performance-based | Revenue Benchmark | Contract Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 47.60% 43.90% 46.60% 43.30%
Cost-plus        
Disaggregation of Revenue [Line Items]        
Revenue $ 312,176 $ 322,823 $ 659,495 $ 662,904
Cost-plus | Revenue Benchmark | Contract Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 25.90% 27.40% 26.90% 28.50%
Fixed price        
Disaggregation of Revenue [Line Items]        
Revenue $ 180,674 $ 158,867 $ 355,747 $ 310,372
Fixed price | Revenue Benchmark | Contract Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 15.00% 13.50% 14.50% 13.30%
Time and materials        
Disaggregation of Revenue [Line Items]        
Revenue $ 139,255 $ 179,426 $ 296,892 $ 347,760
Time and materials | Revenue Benchmark | Contract Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 11.50% 15.20% 12.10% 14.90%