Consolidated Condensed Statements of Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Product revenues	$ 240,056	$ 261,504	$ 741,303	$ 792,490
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Cost of sales	$ 165,364	$ 185,800	$ 518,590	$ 558,452
Gross margin	74,692	75,704	222,713	234,038
Operating expenses:
Net research and development expenses	18,838	19,056	56,990	63,382
Selling, general and administrative expenses	26,861	35,117	91,683	105,803
Restructuring expenses	8,664	5,818	11,809	12,898
Total operating expenses	54,363	59,991	160,482	182,083
Operating income	20,329	15,713	62,231	51,955
Interest expense	(1,148)	(1,241)	(3,756)	(3,661)
Foreign currency gain	4,083	125	3,482	721
Gain on sale of business			4,970
Impairment loss	(837)	(11,476)	(21,206)	(11,476)
Other income	231	212	545	1,538
Earnings before income tax	22,658	3,333	46,266	39,077
Income tax expense	6,771	3,688	19,214	9,807
Net income (loss)	$ 15,887	$ (355)	$ 27,052	$ 29,270
Basic earnings (loss) per share	$ 0.48	$ (0.01)	$ 0.81	$ 0.80
Diluted earnings (loss) per share	$ 0.48	$ (0.01)	$ 0.81	$ 0.80
Weighted average number of shares – basic	32,838,636	36,103,520	33,282,584	36,364,380
Weighted average number of shares – diluted	32,932,679	36,448,162	33,418,555	36,469,759