Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues [Abstract]
Revenues	$ 946,548	$ 747,763	$ 471,496
Cost of revenues
Cost of revenues	766,975	607,899	437,836
Selling, general and administrative expenses	115,127	108,838	88,473
Other operating (income) loss, net	888	(410)	(4,345)
Impairments and other charges	0	0	6,745
Operating income (loss)	63,558	31,436	(57,213)
Foreign currency exchange (gain) loss	1,416	2,051	(710)
Interest expense, net	14,864	13,273	9,866
Gain on extinguishment of debt	0	0	(1,615)
Income (loss) from continuing operations before income taxes	47,278	16,112	(64,754)
Provision (benefit) for income taxes	14,997	4,893	(24,042)
Income (loss) from continuing operations	32,281	11,219	(40,712)
Loss from disposal of discontinued operations, net of tax	0	17,367	0
Net income (loss)	$ 32,281	$ (6,148)	$ (40,712)
Income (loss) per common share - basic:
Income (loss) from continuing operations, basic (in dollars per share)	$ 0.36	$ 0.13	$ (0.49)
Loss from discontinued operations, basic (in dollars per share)	0.00	(0.20)	0.00
Net income (loss), basic (in dollars per share)	0.36	(0.07)	(0.49)
Income (loss) per common share - diluted:
Income (loss) from continuing operations, diluted (in dollars per share)	0.35	0.13	(0.49)
Loss from discontinued operations, diluted (in dollars per share)	0.00	(0.20)	0.00
Net income (loss), diluted (in dollars per share)	$ 0.35	$ (0.07)	$ (0.49)
Product sales [Member]
Revenues [Abstract]
Revenues	$ 743,342	$ 628,401	$ 390,306
Cost of revenues
Cost of revenues	633,847	539,243	386,085
Rental and service [Member]
Revenues [Abstract]
Revenues	203,206	119,362	81,190
Cost of revenues
Cost of revenues	$ 133,128	$ 68,656	$ 51,751