Quarterly report pursuant to Section 13 or 15(d)

Revenue Recognition - Disaggregation of Revenue (Details)

v3.22.1
Revenue Recognition - Disaggregation of Revenue (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Mar. 31, 2022
Mar. 31, 2021
Disaggregation of Revenue [Line Items]        
Revenue $ 1,177,326 $ 959,280 $ 2,328,202 $ 1,904,834
United States        
Disaggregation of Revenue [Line Items]        
Revenue $ 971,365 $ 778,350 $ 1,939,653 $ 1,568,529
United States | Revenue Benchmark | Geographic Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 82.50% 81.10% 83.30% 82.30%
United Kingdom        
Disaggregation of Revenue [Line Items]        
Revenue $ 107,898 $ 72,882 $ 193,705 $ 137,668
United Kingdom | Revenue Benchmark | Geographic Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 9.10% 7.60% 8.30% 7.20%
Australia        
Disaggregation of Revenue [Line Items]        
Revenue $ 46,670 $ 70,947 $ 99,484 $ 126,878
Australia | Revenue Benchmark | Geographic Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 4.00% 7.40% 4.30% 6.70%
Rest of world        
Disaggregation of Revenue [Line Items]        
Revenue $ 51,393 $ 37,101 $ 95,360 $ 71,759
Rest of world | Revenue Benchmark | Geographic Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 4.40% 3.90% 4.10% 3.80%
U.S. state government agencies        
Disaggregation of Revenue [Line Items]        
Revenue $ 411,287 $ 445,697 $ 782,834 $ 833,811
U.S. state government agencies | Revenue Benchmark | Customer Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 35.00% 46.50% 33.70% 43.80%
U.S. federal government agencies        
Disaggregation of Revenue [Line Items]        
Revenue $ 553,707 $ 307,870 $ 1,117,801 $ 693,442
U.S. federal government agencies | Revenue Benchmark | Customer Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 47.00% 32.10% 48.00% 36.40%
International government agencies        
Disaggregation of Revenue [Line Items]        
Revenue $ 194,800 $ 171,700 $ 366,175 $ 319,042
International government agencies | Revenue Benchmark | Customer Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 16.50% 17.90% 15.70% 16.70%
Other, including local municipalities and commercial customers        
Disaggregation of Revenue [Line Items]        
Revenue $ 17,532 $ 34,013 $ 61,392 $ 58,539
Other, including local municipalities and commercial customers | Revenue Benchmark | Customer Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 1.50% 3.50% 2.60% 3.10%
Performance-based        
Disaggregation of Revenue [Line Items]        
Revenue $ 516,210 $ 349,749 $ 1,007,166 $ 643,709
Performance-based | Revenue Benchmark | Contract Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 43.90% 36.40% 43.30% 33.80%
Cost-plus        
Disaggregation of Revenue [Line Items]        
Revenue $ 322,823 $ 286,082 $ 662,904 $ 670,565
Cost-plus | Revenue Benchmark | Contract Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 27.40% 29.80% 28.50% 35.20%
Fixed price        
Disaggregation of Revenue [Line Items]        
Revenue $ 158,867 $ 146,344 $ 310,372 $ 267,121
Fixed price | Revenue Benchmark | Contract Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 13.50% 15.30% 13.30% 14.00%
Time and materials        
Disaggregation of Revenue [Line Items]        
Revenue $ 179,426 $ 177,105 $ 347,760 $ 323,439
Time and materials | Revenue Benchmark | Contract Concentration Risk        
Disaggregation of Revenue [Line Items]        
Revenue in % 15.20% 18.50% 14.90% 17.00%