Consolidated Statements of Operations - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Income Statement [Abstract]        
Net sales $ 199,685 $ 166,685 $ 365,504 $ 328,395
Cost of sales 145,831 120,023 267,069 240,163
Gross profit 53,854 46,662 98,435 88,232
Operating expenses        
Selling, general and administrative expenses 18,935 17,730 36,557 40,878
Research and development expenses 21,005 16,928 40,585 34,886
Restructuring and other gain       (17,010)
Early termination charges   2,262   13,369
Total operating expenses 39,940 36,920 77,142 72,123
Operating income 13,914 9,742 21,293 16,109
Interest expense (5,489) (5,441) (10,952) (10,614)
Foreign currency gain (loss), net (27,449) (11,905) (26,131) 29,881
Other income (expense), net (960) 83 (441) 1,694
Income (loss) before income taxes (19,984) (7,521) (16,231) 37,070
Income tax expenses 1,521 538 2,511 1,391
Net income (loss) $ (21,505) $ (8,059) $ (18,742) $ 35,679
Earnings (loss) per common share-        
Basic $ (0.62) $ (0.24) $ (0.55) $ 1.06
Diluted $ (0.62) $ (0.24) $ (0.55) $ 0.87
Weighted average number of shares-        
Basic 34,420,654 33,952,574 34,337,345 33,808,237
Diluted 34,420,654 33,952,574 34,337,345 43,772,115