Annual report pursuant to Section 13 and 15(d)

Revenue Recognition - Disaggregation of Revenue (Details)

v3.22.2.2
Revenue Recognition - Disaggregation of Revenue (Details) - USD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2022
Sep. 30, 2021
Sep. 30, 2020
Disaggregation of Revenue [Line Items]      
Revenue $ 4,631,018 $ 4,254,485 $ 3,461,537
United States      
Disaggregation of Revenue [Line Items]      
Revenue $ 3,867,354 $ 3,555,394 $ 2,962,611
United States | Revenue Benchmark | Geographic Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 83.50% 83.60% 85.60%
United Kingdom      
Disaggregation of Revenue [Line Items]      
Revenue $ 410,587 $ 286,432 $ 246,334
United Kingdom | Revenue Benchmark | Geographic Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 8.90% 6.70% 7.10%
Australia      
Disaggregation of Revenue [Line Items]      
Revenue $ 173,078 $ 244,995 $ 147,156
Australia | Revenue Benchmark | Geographic Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 3.70% 5.80% 4.30%
Rest of world      
Disaggregation of Revenue [Line Items]      
Revenue $ 179,999 $ 167,664 $ 105,436
Rest of world | Revenue Benchmark | Geographic Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 3.90% 3.90% 3.00%
U. S. federal government agencies      
Disaggregation of Revenue [Line Items]      
Revenue $ 2,189,303 $ 1,805,131 $ 1,559,165
U. S. federal government agencies | Revenue Benchmark | Customer Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 47.30% 42.40% 45.10%
U.S. state government agencies      
Disaggregation of Revenue [Line Items]      
Revenue $ 1,605,457 $ 1,654,555 $ 1,344,227
U.S. state government agencies | Revenue Benchmark | Customer Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 34.70% 38.90% 38.80%
International government agencies      
Disaggregation of Revenue [Line Items]      
Revenue $ 722,192 $ 663,180 $ 467,185
International government agencies | Revenue Benchmark | Customer Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 15.60% 15.60% 13.50%
Other, including local municipalities and commercial customers      
Disaggregation of Revenue [Line Items]      
Revenue $ 114,066 $ 131,619 $ 90,960
Other, including local municipalities and commercial customers | Revenue Benchmark | Customer Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 2.40% 3.10% 2.60%
Performance-based      
Disaggregation of Revenue [Line Items]      
Revenue $ 2,091,608 $ 1,416,562 $ 1,109,153
Performance-based | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 45.20% 33.30% 32.10%
Cost-plus      
Disaggregation of Revenue [Line Items]      
Revenue $ 1,248,759 $ 1,237,995 $ 1,578,912
Cost-plus | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 27.00% 29.10% 45.60%
Fixed price      
Disaggregation of Revenue [Line Items]      
Revenue $ 627,402 $ 553,645 $ 471,505
Fixed price | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 13.50% 13.00% 13.60%
Time and materials      
Disaggregation of Revenue [Line Items]      
Revenue $ 663,249 $ 1,046,283 $ 301,967
Time and materials | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 14.30% 24.60% 8.70%
Program Operations      
Disaggregation of Revenue [Line Items]      
Revenue $ 2,596,801 $ 2,755,820 $ 2,395,618
Program Operations | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 56.10% 64.80% 69.20%
Clinical Services      
Disaggregation of Revenue [Line Items]      
Revenue $ 1,176,081 $ 699,424 $ 539,018
Clinical Services | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 25.40% 16.40% 15.60%
Employment & Other      
Disaggregation of Revenue [Line Items]      
Revenue $ 551,755 $ 463,695 $ 318,431
Employment & Other | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 11.90% 10.90% 9.20%
Technology Solutions      
Disaggregation of Revenue [Line Items]      
Revenue $ 306,381 $ 335,546 $ 208,470
Technology Solutions | Revenue Benchmark | Contract Concentration Risk      
Disaggregation of Revenue [Line Items]      
Revenue in % 6.60% 7.90% 6.00%