Annual report pursuant to Section 13 and 15(d)

Revenue Recognition - Disaggregation of Revenue (Details)

v3.23.3
Revenue Recognition - Disaggregation of Revenue (Details) - USD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2021
Disaggregation of Revenue [Line Items]      
Revenue $ 4,904,728 $ 4,631,018 $ 4,254,485
U. S. federal government agencies      
Disaggregation of Revenue [Line Items]      
Revenue $ 2,344,863 $ 2,189,303 $ 1,805,131
U. S. federal government agencies | Revenue Benchmark | Customer Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 47.80% 47.30% 42.40%
U.S. state government agencies      
Disaggregation of Revenue [Line Items]      
Revenue $ 1,800,814 $ 1,605,457 $ 1,654,555
U.S. state government agencies | Revenue Benchmark | Customer Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 36.70% 34.70% 38.90%
International government agencies      
Disaggregation of Revenue [Line Items]      
Revenue $ 663,044 $ 722,192 $ 663,180
International government agencies | Revenue Benchmark | Customer Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 13.50% 15.60% 15.60%
Other, including local municipalities and commercial customers      
Disaggregation of Revenue [Line Items]      
Revenue $ 96,007 $ 114,066 $ 131,619
Other, including local municipalities and commercial customers | Revenue Benchmark | Customer Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 2.00% 2.50% 3.10%
Performance-based      
Disaggregation of Revenue [Line Items]      
Revenue $ 2,425,597 $ 2,091,608 $ 1,416,562
Performance-based | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 49.50% 45.20% 33.30%
Cost-plus      
Disaggregation of Revenue [Line Items]      
Revenue $ 1,238,574 $ 1,248,759 $ 1,237,995
Cost-plus | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 25.30% 27.00% 29.10%
Fixed price      
Disaggregation of Revenue [Line Items]      
Revenue $ 717,167 $ 627,402 $ 553,645
Fixed price | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 14.60% 13.50% 13.00%
Time and materials      
Disaggregation of Revenue [Line Items]      
Revenue $ 523,390 $ 663,249 $ 1,046,283
Time and materials | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 10.70% 14.30% 24.60%
Program Operations      
Disaggregation of Revenue [Line Items]      
Revenue $ 2,607,263 $ 2,596,801 $ 2,755,820
Program Operations | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 53.20% 56.10% 64.80%
Clinical Services      
Disaggregation of Revenue [Line Items]      
Revenue $ 1,486,040 $ 1,176,081 $ 699,424
Clinical Services | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 30.30% 25.40% 16.40%
Employment & Other      
Disaggregation of Revenue [Line Items]      
Revenue $ 520,981 $ 551,755 $ 463,695
Employment & Other | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 10.60% 11.90% 10.90%
Technology Solutions      
Disaggregation of Revenue [Line Items]      
Revenue $ 290,444 $ 306,381 $ 335,546
Technology Solutions | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 5.90% 6.60% 7.90%