Description of Business and Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands |
3 Months Ended | 9 Months Ended | ||||
|---|---|---|---|---|---|---|
|
Sep. 28, 2018
USD ($)
|
Sep. 29, 2017
USD ($)
|
Sep. 28, 2018
USD ($)
segment
|
Sep. 29, 2017
USD ($)
|
Jan. 23, 2018 |
Dec. 31, 2017
USD ($)
|
|
| Accounting Policies [Line Items] | ||||||
| Number of reportable segments | segment | 1 | |||||
| Revenue | $ 308,095 | $ 269,625 | $ 949,744 | $ 819,005 | ||
| Total revenue | Credit risk | U.S. Army | ||||||
| Accounting Policies [Line Items] | ||||||
| Concentration risk, percentage | 74.00% | 83.00% | ||||
| High Desert Support Services (HDSS) | ||||||
| Accounting Policies [Line Items] | ||||||
| Ownership percentage | 40.00% | 40.00% | ||||
| Investment balance | $ 2,100 | $ 2,100 | $ 1,700 | |||
| SENTEL | ||||||
| Accounting Policies [Line Items] | ||||||
| Percentage of outstanding common stock acquired | 100.00% | |||||