| Disaggregation of Revenue | 
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | Table 4.1: Revenue by Contract Type |  
|  | For the Three Months Ended |  | For the Nine Months Ended |  
|  | June 30, 2022 |  | June 30, 2021 |  | June 30, 2022 |  | June 30, 2021 |  
|  | Amount |  | % |  | Amount |  | % |  | Amount |  | % |  | Amount |  | % |  
|  | (dollars in thousands) |  
| Performance-based | $ | 520,202 |  |  | 46.2 % |  | $ | 389,800 |  |  | 31.3 % |  | $ | 1,527,368 |  |  | 44.2 % |  | $ | 1,033,509 |  |  | 32.8 % |  
| Cost-plus | 282,578 |  |  | 25.1 % |  | 282,808 |  |  | 22.7 % |  | 945,482 |  |  | 27.4 % |  | 953,373 |  |  | 30.3 % |  
| Fixed price | 160,219 |  |  | 14.2 % |  | 146,175 |  |  | 11.8 % |  | 470,591 |  |  | 13.6 % |  | 413,296 |  |  | 13.1 % |  
| Time and materials | 162,786 |  |  | 14.5 % |  | 424,737 |  |  | 34.2 % |  | 510,546 |  |  | 14.8 % |  | 748,176 |  |  | 23.8 % |  
| Total revenue | $ | 1,125,785 |  |  |  |  | $ | 1,243,520 |  |  |  |  | $ | 3,453,987 |  |  |  |  | $ | 3,148,354 |  |  |  | 
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | Table 4.2: Revenue by Customer Type |  
|  | For the Three Months Ended |  | For the Nine Months Ended |  
|  | June 30, 2022 |  | June 30, 2021 |  | June 30, 2022 |  | June 30, 2021 |  
|  | Amount |  | % |  | Amount |  | % |  | Amount |  | % |  | Amount |  | % |  
|  | (dollars in thousands) |  
| U.S. state government agencies | $ | 401,042 |  |  | 35.7 % |  | $ | 431,987 |  |  | 34.7 % |  | $ | 1,183,876 |  |  | 34.3 % |  | $ | 1,265,798 |  |  | 40.2 % |  
| U.S. federal government agencies | 507,047 |  |  | 45.0 % |  | 594,771 |  |  | 47.8 % |  | 1,624,848 |  |  | 47.0 % |  | 1,288,213 |  |  | 40.9 % |  
| International government agencies | 191,753 |  |  | 17.0 % |  | 180,049 |  |  | 14.5 % |  | 557,928 |  |  | 16.2 % |  | 499,091 |  |  | 15.9 % |  
| Other, including local municipalities and commercial customers | 25,943 |  |  | 2.3 % |  | 36,713 |  |  | 3.0 % |  | 87,335 |  |  | 2.5 % |  | 95,252 |  |  | 3.0 % |  
| Total revenue | $ | 1,125,785 |  |  |  |  | $ | 1,243,520 |  |  |  |  | $ | 3,453,987 |  |  |  |  | $ | 3,148,354 |  |  |  | 
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | Table 4.3: Revenue by Geography |  
|  | For the Three Months Ended |  | For the Nine Months Ended |  
|  | June 30, 2022 |  | June 30, 2021 |  | June 30, 2022 |  | June 30, 2021 |  
|  | Amount |  | % |  | Amount |  | % |  | Amount |  | % |  | Amount |  | % |  
|  | (dollars in thousands) |  
| United States | $ | 924,839 |  |  | 82.2 % |  | $ | 1,053,940 |  |  | 84.8 % |  | $ | 2,864,492 |  |  | 83.0 % |  | $ | 2,622,469 |  |  | 83.3 % |  
| United Kingdom | 109,776 |  |  | 9.7 % |  | 74,109 |  |  | 6.0 % |  | 303,481 |  |  | 8.8 % |  | 211,777 |  |  | 6.7 % |  
| Australia | 43,594 |  |  | 3.9 % |  | 65,283 |  |  | 5.2 % |  | 143,078 |  |  | 4.1 % |  | 192,161 |  |  | 6.1 % |  
| Rest of world | 47,576 |  |  | 4.2 % |  | 50,188 |  |  | 4.0 % |  | 142,936 |  |  | 4.1 % |  | 121,947 |  |  | 3.9 % |  
| Total revenue | $ | 1,125,785 |  |  |  |  | $ | 1,243,520 |  |  |  |  | $ | 3,453,987 |  |  |  |  | $ | 3,148,354 |  |  |  |  |