Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating Income (Loss) [Abstract]
Revenues	$ 236,262	$ 183,020	$ 463,555	$ 341,711
Cost of revenues	188,480	148,431	374,935	278,021
Selling, general and administrative expenses	28,708	26,630	55,662	52,027
Other operating income, net	(69)	(9)	(23)	(51)
Operating income	19,143	7,968	32,981	11,714
Foreign currency exchange loss	458	534	683	926
Interest expense, net	3,691	3,441	6,991	6,659
Income from operations before income taxes	14,994	3,993	25,307	4,129
Provision for income taxes	4,148	2,361	7,239	3,480
Net income	$ 10,846	$ 1,632	$ 18,068	$ 649
Income per common share - basic (in dollars per share)	$ 0.12	$ 0.02	$ 0.20	$ 0.01
Income per common share - diluted (in dollars per share)	$ 0.12	$ 0.02	$ 0.19	$ 0.01