Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Revenue Disaggregated by Geographic Location and Contract Type (Details)

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Summary of Significant Accounting Policies - Revenue Disaggregated by Geographic Location and Contract Type (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Disaggregation of Revenue [Line Items]        
Revenues $ 3,353,278 $ 3,020,161 $ 9,056,675 $ 8,290,487
Percent of total revenues 100.00% 100.00% 100.00% 100.00%
Unit-price contracts        
Disaggregation of Revenue [Line Items]        
Revenues $ 1,399,358 $ 1,141,102 $ 3,593,644 $ 3,034,169
Percent of total revenues 41.80% 37.70% 39.70% 36.60%
Cost-plus contracts        
Disaggregation of Revenue [Line Items]        
Revenues $ 825,622 $ 702,392 $ 2,247,879 $ 1,958,404
Percent of total revenues 24.60% 23.30% 24.80% 23.60%
Fixed price contracts        
Disaggregation of Revenue [Line Items]        
Revenues $ 1,128,298 $ 1,176,667 $ 3,215,152 $ 3,297,914
Percent of total revenues 33.60% 39.00% 35.50% 39.80%
United States        
Disaggregation of Revenue [Line Items]        
Revenues $ 2,892,446 $ 2,629,606 $ 7,669,360 $ 7,105,568
Percent of total revenues 86.20% 87.10% 84.70% 85.70%
Canada        
Disaggregation of Revenue [Line Items]        
Revenues $ 382,072 $ 320,576 $ 1,123,077 $ 917,621
Percent of total revenues 11.40% 10.60% 12.40% 11.10%
Australia        
Disaggregation of Revenue [Line Items]        
Revenues $ 52,804 $ 49,537 $ 170,719 $ 156,664
Percent of total revenues 1.60% 1.60% 1.90% 1.90%
Others        
Disaggregation of Revenue [Line Items]        
Revenues $ 25,956 $ 20,442 $ 93,519 $ 110,634
Percent of total revenues 0.80% 0.70% 1.00% 1.30%