Revenue - Revenue by Contract Type (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 27, 2019 |
Sep. 28, 2018 |
Sep. 27, 2019 |
Sep. 28, 2018 |
|
| Disaggregation of Revenue [Line Items] | ||||
| Total revenue | $ 359,854 | $ 308,095 | $ 1,017,371 | $ 949,744 |
| Cost-plus and cost-reimbursable | ||||
| Disaggregation of Revenue [Line Items] | ||||
| Total revenue | 272,810 | 240,338 | 781,024 | 713,289 |
| Firm-fixed-price | ||||
| Disaggregation of Revenue [Line Items] | ||||
| Total revenue | $ 87,044 | $ 67,757 | $ 236,347 | $ 236,455 |