Customer Concentrations (Tables)

12 Months Ended

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.