Business Segments and Customer Information - Major Customers (Details) - USD ($) $ in Thousands |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2018 |
Sep. 30, 2018 |
Jun. 30, 2018 |
Mar. 31, 2018 |
Dec. 31, 2017 |
Sep. 30, 2017 |
Jun. 30, 2017 |
Mar. 31, 2017 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Revenue, Major Customer [Line Items] | |||||||||||
| Revenues | $ 180,996 | $ 168,931 | $ 170,394 | $ 176,897 | $ 194,795 | $ 174,164 | $ 193,860 | $ 197,294 | $ 697,218 | $ 760,113 | $ 691,790 |
| Percentage of revenue by customer | 100.00% | 100.00% | 100.00% | ||||||||
| USPS | |||||||||||
| Revenue, Major Customer [Line Items] | |||||||||||
| Revenues | $ 175,339 | $ 180,205 | $ 181,215 | ||||||||
| Percentage of revenue by customer | 25.10% | 23.70% | 26.20% | ||||||||
| U.S. Navy | |||||||||||
| Revenue, Major Customer [Line Items] | |||||||||||
| Revenues | $ 160,952 | $ 206,644 | $ 190,155 | ||||||||
| Percentage of revenue by customer | 23.10% | 27.20% | 27.50% | ||||||||
| U.S. Army | |||||||||||
| Revenue, Major Customer [Line Items] | |||||||||||
| Revenues | $ 156,519 | $ 188,462 | $ 139,764 | ||||||||
| Percentage of revenue by customer | 22.50% | 24.80% | 20.20% | ||||||||
| U.S. Air Force | |||||||||||
| Revenue, Major Customer [Line Items] | |||||||||||
| Revenues | $ 17,023 | $ 7,123 | $ 3,482 | ||||||||
| Percentage of revenue by customer | 2.40% | 0.90% | 0.50% | ||||||||
| Total - DoD | |||||||||||
| Revenue, Major Customer [Line Items] | |||||||||||
| Revenues | $ 334,494 | $ 402,229 | $ 333,401 | ||||||||
| Percentage of revenue by customer | 48.00% | 52.90% | 48.20% | ||||||||
| Commercial Aviation | |||||||||||
| Revenue, Major Customer [Line Items] | |||||||||||
| Revenues | $ 135,864 | $ 126,960 | $ 131,067 | ||||||||
| Percentage of revenue by customer | 19.50% | 16.70% | 19.00% | ||||||||
| Other Commercial | |||||||||||
| Revenue, Major Customer [Line Items] | |||||||||||
| Revenues | $ 14,742 | $ 12,498 | $ 10,721 | ||||||||
| Percentage of revenue by customer | 2.10% | 1.70% | 1.50% | ||||||||
| Total - Commercial | |||||||||||
| Revenue, Major Customer [Line Items] | |||||||||||
| Revenues | $ 150,606 | $ 139,458 | $ 141,788 | ||||||||
| Percentage of revenue by customer | 21.60% | 18.40% | 20.50% | ||||||||
| Other Government | |||||||||||
| Revenue, Major Customer [Line Items] | |||||||||||
| Revenues | $ 36,779 | $ 38,221 | $ 35,386 | ||||||||
| Percentage of revenue by customer | 5.30% | 5.00% | 5.10% | ||||||||