CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net income	$ 73,951	$ 31,234	$ 10,793
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Lower of cost or market reserve adjustment to inventory	1,866	3,707	2,832
Depreciation and amortization	20,381	14,188	9,424
Deferred income taxes, net	(114)	(11,426)
Loss on disposal of assets	97	126	78
Share-based compensation	7,795	3,833	2,120
Unrealized foreign exchange loss (gain)	330	(937)	2,462
Changes in operating assets and liabilities:
Accounts receivable, trade	(10,080)	(11,147)	(7,531)
Notes receivable			977
Prepaid tax	(1,386)
Inventories	(21,876)	10,207	(37,502)
Other current assets	(4,185)	4,119	(2,624)
Accounts payable	7,249	9,105	(1,258)
Accrued income taxes	6,204	988	220
Accrued liabilities	4,052	3,107	4,797
Net cash provided by (used in) operating activities	84,284	57,104	(15,212)
Investing activities:
Purchase of short-term investments			(175)
Maturities of short-term investments	8	7,752
Purchase of property, plant and equipment	(66,968)	(49,442)	(57,080)
Proceeds from disposal of equipment	171	14	351
Deposits and prepaid for equipment	(2,871)	688	(4,238)
Purchase of intangible assets	(499)	(547)	(478)
Net cash used in investing activities	(70,159)	(41,535)	(61,620)
Financing activities:
Proceeds from issuance notes payable and long-term debt		28,858	16,944
Principal payments of long-term debt and notes payable	(42,758)	(5,855)	(2,413)
Proceeds from line of credit borrowings	88,003	117,172	144,386
Repayments of line of credit borrowings	(39,003)	(163,068)	(121,386)
Proceeds from bank acceptance payable		5,850	8,257
Repayments of bank acceptance payable	(309)	(8,398)	(6,361)
Repayments of notes payable		(1,000)	(1,000)
Exercise of stock options	1,460	859	452
Payments of tax withholding on behalf of employees related to share-based compensation	(10,721)
Proceeds from common stock offering, net	21,572	27,237	38,648
Other			6
Net cash provided by financing activities	18,244	1,655	77,533
Effect of exchange rate changes on cash	(385)	1,947	(592)
Net increase in cash, cash equivalents and restricted cash	31,984	19,171	109
Cash, cash equivalents and restricted cash, at beginning of period	51,964	32,793	32,684
Cash, cash equivalents and restricted cash, at end of period	83,948	51,964	32,793
Cash paid for:
Interest	872	1,689	1,070
Income taxes	$ 5,835	$ (12)	$ 650