Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Income (Loss) [Abstract]
Revenues	$ 235,329	$ 201,663	$ 698,884	$ 543,374
Cost of revenues	194,730	164,587	569,665	442,608
Selling, general and administrative expenses	29,820	27,270	85,482	79,297
Other operating (income) loss, net	725	(76)	702	(127)
Operating income	10,054	9,882	43,035	21,596
Foreign currency exchange (gain) loss	(89)	174	594	1,100
Interest expense, net	3,668	3,586	10,659	10,245
Income from operations before income taxes	6,475	6,122	31,782	10,251
Provision for income taxes	2,831	3,469	10,070	6,949
Net income	$ 3,644	$ 2,653	$ 21,712	$ 3,302
Income per common share - basic (in dollars per share)	$ 0.04	$ 0.03	$ 0.24	$ 0.04
Income per common share - diluted (in dollars per share)	$ 0.04	$ 0.03	$ 0.23	$ 0.04