| Segment Information | 
Our segment information is as follows (in thousands): 
 
| For the years ended December 31, |  |  |  |  |  |  |  |  |  |  
|  |  | 2015 |  |  | 2014 |  |  | 2013 |  |  
| Revenues |  |  |  |  |  |  |  |  |  |  
|   Supply Chain Management Group |  | $ | 196,772 |  |  | $ | 172,482 |  |  | $ | 154,702 |  |  
|   Aviation Group |  |  | 119,729 |  |  |  | - |  |  |  | - |  |  
|   Federal Services Group |  |  | 166,973 |  |  |  | 190,761 |  |  |  | 242,343 |  |  
|   IT, Energy and Management Consulting Group |  |  | 50,508 |  |  |  | 60,828 |  |  |  | 74,593 |  |  
|     Total revenues |  | $ | 533,982 |  |  | $ | 424,071 |  |  | $ | 471,638 |  |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Operating income: |  |  |  |  |  |  |  |  |  |  |  |  |  
|   Supply Chain Management Group |  | $ | 35,453 |  |  | $ | 29,694 |  |  | $ | 27,299 |  |  
|   Aviation Group |  |  | 10,635 |  |  |  | - |  |  |  | - |  |  
|   Federal Services Group |  |  | 2,071 |  |  |  | 3,452 |  |  |  | 9,469 |  |  
|   IT, Energy and Management Consulting Group |  |  | 4,731 |  |  |  | 6,634 |  |  |  | 9,061 |  |  
|   Corporate |  |  | (2,351 | ) |  |  | (2,850 | ) |  |  | (1,726 | ) |  
|     Operating income |  | $ | 50,539 |  |  | $ | 36,930 |  |  | $ | 44,103 |  |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Depreciation and amortization expense: |  |  |  |  |  |  |  |  |  |  |  |  |  
|   Supply Chain Management Group |  | $ | 7,074 |  |  | $ | 5,373 |  |  | $ | 4,265 |  |  
|   Aviation Group |  |  | 5,865 |  |  |  | - |  |  |  | - |  |  
|   Federal Services Group |  |  | 10,635 |  |  |  | 11,320 |  |  |  | 13,356 |  |  
|   IT, Energy and Management Consulting Group |  |  | 1,967 |  |  |  | 2,077 |  |  |  | 2,387 |  |  
|     Total depreciation and amortization |  | $ | 25,541 |  |  | $ | 18,770 |  |  | $ | 20,008 |  |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Capital expenditures: |  |  |  |  |  |  |  |  |  |  |  |  |  
|   Supply Chain Management Group |  | $ | 7,544 |  |  | $ | 2,524 |  |  | $ | 895 |  |  
|   Aviation Group |  |  | 959 |  |  |  | - |  |  |  | - |  |  
|   Federal Services Group |  |  | 78 |  |  |  | 230 |  |  |  | 1,447 |  |  
|   IT, Energy and Management Consulting Group |  |  | 16 |  |  |  | 199 |  |  |  | 71 |  |  
|   Corporate |  |  | 1,965 |  |  |  | 461 |  |  |  | 2,003 |  |  
|     Total capital expenditures |  | $ | 10,562 |  |  | $ | 3,414 |  |  | $ | 4,416 |  |  
 
|  |  | December 31, |  |  
|  |  | 2015 |  |  | 2014 |  |  
| Total assets: |  |  |  |  |  |  |  
|   Supply Chain Management Group |  | $ | 189,654 |  |  | $ | 192,720 |  |  
|   Aviation Group |  |  | 264,160 |  |  |  | - |  |  
|   Federal Services Group |  |  | 38,626 |  |  |  | 36,225 |  |  
|   IT, Energy and Management Consulting Group |  |  | 47,107 |  |  |  | 49,790 |  |  
|   Corporate |  |  | 82,587 |  |  |  | 76,595 |  |  
|     Total assets |  | $ | 622,134 |  |  | $ | 355,330 |  |  | 
| Revenue by Customer | 
Our customers also include various other government agencies and commercial entities. Our revenue by customer is as follows for the years ended December 31, (in thousands):   
|  |  | Revenues by Customer |  |  
|  |  | (dollars in thousands) |  |  
|  |  | Years ended December 31, |  |  
| Customer |  | 2015 |  |  | % |  |  | 2014 |  |  | % |  |  | 2013 |  |  | % |  |  
| U. S. Postal Service |  | $ | 184,876 |  |  |  | 34.6 |  |  | $ | 167,268 |  |  |  | 39.4 |  |  | $ | 142,203 |  |  |  | 30.1 |  |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| U.S. Army |  |  | 80,086 |  |  |  | 15.0 |  |  |  | 101,714 |  |  |  | 24.0 |  |  |  | 101,736 |  |  |  | 21.6 |  |  
| U.S. Navy |  |  | 98,887 |  |  |  | 18.5 |  |  |  | 88,007 |  |  |  | 20.7 |  |  |  | 123,307 |  |  |  | 26.1 |  |  
| U.S. Air Force |  |  | 3,558 |  |  |  | 0.7 |  |  |  | 3,323 |  |  |  | 0.8 |  |  |  | 3,625 |  |  |  | 0.8 |  |  
| Total - DoD |  |  | 182,531 |  |  |  | 34.2 |  |  |  | 193,044 |  |  |  | 45.5 |  |  |  | 228,668 |  |  |  | 48.5 |  |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Commercial Aviation |  |  | 119,729 |  |  |  | 22.4 |  |  |  | - |  |  |  | - |  |  |  | - |  |  |  | - |  |  
| Other Commercial |  |  | 4,653 |  |  |  | 0.9 |  |  |  | 3,680 |  |  |  | 0.9 |  |  |  | 2,250 |  |  |  | 0.5 |  |  
| Total - Commercial |  |  | 124,382 |  |  |  | 23.3 |  |  |  | 3,680 |  |  |  | 0.9 |  |  |  | 2,250 |  |  |  | 0.5 |  |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Department of Energy |  |  | 16,020 |  |  |  | 3.0 |  |  |  | 19,000 |  |  |  | 4.5 |  |  |  | 20,124 |  |  |  | 4.3 |  |  
| Social Security Administration |  |  | 9,666 |  |  |  | 1.8 |  |  |  | 10,153 |  |  |  | 2.4 |  |  |  | 12,981 |  |  |  | 2.8 |  |  
| Department of Treasury |  |  | 1,405 |  |  |  | 0.3 |  |  |  | 10,897 |  |  |  | 2.6 |  |  |  | 35,929 |  |  |  | 7.6 |  |  
| Other Government |  |  | 15,102 |  |  |  | 2.8 |  |  |  | 20,029 |  |  |  | 4.7 |  |  |  | 29,483 |  |  |  | 6.2 |  |  
| Total - Other Civilian Agencies |  |  | 42,193 |  |  |  | 7.9 |  |  |  | 60,079 |  |  |  | 14.2 |  |  |  | 98,517 |  |  |  | 20.9 |  |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Total |  | $ | 533,982 |  |  |  | 100.0 |  |  | $ | 424,071 |  |  |  | 100.0 |  |  | $ | 471,638 |  |  |  | 100.0 |  |  |