CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Net sales	$ 153,133	$ 193,896	$ 304,911	$ 378,059
Cost of sales	115,058	159,903	223,895	304,192
Gross profit	38,075	33,993	81,016	73,867
Research and development expenses	7,385	7,163	15,283	13,954
Selling, general and administrative expenses	24,230	30,756	51,227	62,176
Operating income (loss)	6,460	(3,926)	14,506	(2,263)
Interest income (expense), net	(372)	(1,098)	(1,004)	(2,304)
Accrued social insurance adjustment	9,464	0	9,464	0
Other income (expense), net	731	188	383	(278)
Income (loss) before provision for income taxes	16,283	(4,836)	23,349	(4,845)
Provision for income taxes	1,883	225	3,103	1,221
Net income (loss)	$ 14,400	$ (5,061)	$ 20,246	$ (6,066)
Earnings (loss) per share:
Basic (in dollars per share)	$ 1.03	$ (0.37)	$ 1.45	$ (0.44)
Diluted (in dollars per share)	$ 1.02	$ (0.37)	$ 1.43	$ (0.44)
Shares used in computing earnings (loss) per share:
Basic (in shares)	13,915	13,863	13,938	13,845
Diluted (in shares)	14,151	13,863	14,181	13,845