Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenues	$ 216,412	$ 236,262	$ 427,885	$ 463,555
Cost of revenues	177,933	188,480	352,909	374,935
Selling, general and administrative expenses	28,037	28,708	58,779	55,662
Other operating income, net	(472)	(69)	(396)	(23)
Operating income	10,914	19,143	16,593	32,981
Foreign currency exchange (gain) loss	990	458	(72)	683
Interest expense, net	3,523	3,691	7,179	6,991
Income before income taxes	6,401	14,994	9,486	25,307
Provision for income taxes	2,095	4,148	3,898	7,239
Net income	$ 4,306	$ 10,846	$ 5,588	$ 18,068
Net income per common share - basic (in dollars per share)	$ 0.05	$ 0.12	$ 0.06	$ 0.20
Net income per common share - diluted (in dollars per share)	$ 0.05	$ 0.12	$ 0.06	$ 0.19