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 | ||