Quarterly report pursuant to Section 13 or 15(d)

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

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Summary of Significant Accounting Policies - Revenue Disaggregated by Geographic Location and Contract Type (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Disaggregation of Revenue [Line Items]        
Revenues $ 2,985,281 $ 2,609,307 $ 8,059,205 $ 6,987,851
Unit-price contracts        
Disaggregation of Revenue [Line Items]        
Revenues 1,082,858   2,714,441  
Fixed price contracts        
Disaggregation of Revenue [Line Items]        
Revenues 1,239,666   3,497,746  
Cost-plus contracts        
Disaggregation of Revenue [Line Items]        
Revenues 662,757   1,847,018  
United States        
Disaggregation of Revenue [Line Items]        
Revenues 2,317,643   6,223,507  
Canada        
Disaggregation of Revenue [Line Items]        
Revenues 522,618   1,376,149  
Australia        
Disaggregation of Revenue [Line Items]        
Revenues 75,055   308,392  
Latin America and Other        
Disaggregation of Revenue [Line Items]        
Revenues $ 69,965   $ 151,157