Consolidated Condensed Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Product revenues	$ 258,939	$ 235,853	$ 784,607	$ 728,498
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Cost of sales	$ 185,800	$ 165,667	$ 558,452	$ 494,843
Gross margin	73,139	70,186	226,155	233,655
Operating expenses:
Net research and development expenses	19,056	19,721	63,382	60,633
Selling, general and administrative expenses	32,552	34,331	97,920	96,912
Restructuring expenses	5,818		12,898
Total operating expenses	57,426	54,052	174,200	157,545
Operating income	15,713	16,134	51,955	76,110
Interest expense	(1,241)	(1,250)	(3,661)	(3,633)
Foreign currency gain (loss)	125	(7,340)	721	(21,920)
Impairment loss	(11,476)		(11,476)
Other income (loss)	212	(360)	1,538	145
Earnings before income tax	3,333	7,184	39,077	50,702
Income tax expense	3,688	630	9,807	10,233
Net income (loss)	$ (355)	$ 6,554	$ 29,270	$ 40,469
Basic earnings (loss) per share	$ (0.01)	$ 0.18	$ 0.80	$ 1.10
Diluted earnings (loss) per share	$ (0.01)	$ 0.18	$ 0.80	$ 1.10
Weighted average number of shares – basic	36,103,520	36,742,168	36,364,380	36,713,294
Weighted average number of shares – diluted	36,448,162	36,805,076	36,469,759	36,831,213