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Customer Concentrations (Tables) | 12 Months Ended
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Dec. 31, 2017
Customer Concentrations |
Schedule of revenue from customers | During the years ended December 31, 2017, 2016 and 2015, we generated 38.4%, 45.6% and 48.9%, of our revenues, respectively, from the following customers (in thousands):
|  |  |  | 2017 |  | 2016 |  | 2015 |
Description of Customer's Business |  | Segment |  | Amount |  | Percentage |  | Amount |  | Percentage |  | Amount |  | Percentage |
State DOT |  | Civil |  | $ | 222,142 |  | 9.3% |  | $ | 193,049 |  | 9.7% |  | $ | 183,847 |  | 9.5% |
Public gas and electric utility |  | Utilities |  |  | 210,747 |  | 8.9% |  |  | 184,002 |  | 9.2% |  |  | 120,507 |  | 6.2% |
Private gas and electric utility |  | Utilities |  |  | 190,659 |  | 8.0% |  |  | 201,443 |  | 10.1% |  |  | 173,232 |  | 9.0% |
Chemical/Energy producer |  | Power/Civil |  |  | 160,995 |  | 6.8% |  |  | 208,458 |  | 10.4% |  |  | 173,931 |  | 9.0% |
Pipeline operator |  | Pipeline |  |  | 128,182 |  | 5.4% |  |  | * |  | * |  |  | * |  | * |
Pipeline operator |  | Pipeline |  |  | * |  | * |  |  | 123,055 |  | 6.2% |  |  | * |  | * |
Pipeline operator |  | Pipeline |  |  | * |  | * |  |  | * |  | * |  |  | 165,578 |  | 8.6% |
Gas utility |  | Utilities |  |  | * |  | * |  |  | * |  | * |  |  | 127,128 |  | 6.6% |
|  |  |  | $ | 912,725 |  | 38.4% |  | $ | 910,007 |  | 45.6% |  | $ | 944,223 |  | 48.9% |
(*)Indicates a customer with less than 5% of revenues during such period.

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