CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CONSOLIDATED STATEMENTS OF OPERATIONS [Abstract]
Net sales	$ 1,171,599	$ 1,184,739	$ 1,147,431
Cost of sales	1,035,833	941,610	882,162
Gross profit	135,766	243,129	265,269
Selling, general and administrative expenses	180,795	160,775	153,145
Research and development expenses	28,332	26,817	24,969
Restructuring and asset impairment charges	13,060	0	0
Income (loss) from operations	(86,421)	55,537	87,155
Other income:
Interest expense	(1,045)	(840)	(1,395)
Interest income	952	1,302	806
Other income	536	1,218	529
Income (loss) before income taxes	(85,978)	57,217	87,095
Income tax provision (benefit)	(25,234)	19,627	32,107
Net income (loss)	(60,744)	37,590	54,988
Net loss attributable to non-controlling interest	295	205	171
Net income (loss) attributable to controlling interest	$ (60,449)	$ 37,795	$ 55,159
Net income (loss) attributable to controlling interest:
Basic (in dollars per share)	$ (2.64)	$ 1.64	$ 2.40
Diluted (in dollars per share)	$ (2.64)	$ 1.63	$ 2.38
Weighted average number of common shares outstanding:
Basic (in shares)	22,902	23,025	22,992
Diluted (in shares)	22,902	23,184	23,142