CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income (loss)		$ (1,588)	$ 11,009	$ 10,061
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization		5,531	4,871	4,422
Amortization of marketable securities premium		37	158	173
Impairment charge on equity investee		1,068		313
Stock-based compensation		2,346	1,925	1,405
Realized gain on sale of available-for-sale securities				(77)
Loss (gain) on disposal of equipment		72	(99)	57
Gain from deconsolidation of a subsidiary		(175)
Loss from equity method investments, net		983	1,080	1,381
Return on equity method investments		362
Changes in operating assets and liabilities:
Accounts receivable		441	2,819	(7,977)
Inventories		8,862	(14,629)	(4,740)
Prepaid expenses and other current assets		2,936	(4,600)	(2,309)
Other assets		(1,188)	(1,888)	(52)
Accounts payable		(3,137)	2,314	4,401
Accrued liabilities *	[1]	(4,010)	518	1,642
Other long-term liabilities, including royalties		118	(260)	(85)
Net cash provided by operating activities		12,658	3,218	8,615
Cash flows from investing activities:
Purchases of property, plant and equipment		(21,792)	(40,539)	(21,356)
Proceeds from sale of equipment			99
Purchases of available-for-sale securities		(8,725)	(9,937)	(30,021)
Proceeds from sales and maturities of available-for-sale securities		22,189	19,550	14,750
Repayment of related party notes receivable				169
Net cash used in investing activities		(8,328)	(30,827)	(36,458)
Cash flows from financing activities:
Proceeds from common stock options exercised		268	628	34,338
Proceeds from sale of subsidiary shares to noncontrolling interests, net of portion allocated to noncontrolling interests		366		1,765
Consideration paid to repurchase subsidiary shares from noncontrolling interests		(262)	(415)
Proceeds from short-term loan		5,814
Dividends paid by joint ventures to their minority shareholders				(465)
Net cash provided by financing activities		6,186	213	35,638
Effect of exchange rate changes on cash and cash equivalents		(150)	(430)	405
Net increase (decrease) in cash and cash equivalents		10,366	(27,826)	8,200
Cash and cash equivalents at the beginning of the year		16,526	44,352	36,152
Cash and cash equivalents at the end of the year		26,892	16,526	44,352
Supplemental disclosures:
Income taxes paid, net of refunds		749	1,134	$ 714
Supplemental disclosure of non-cash flow information:
Consideration payable to repurchase subsidiary shares from noncontrolling interests, included in accrued liabilities		151	1,192
Reduction of noncontrolling interests in excess (deficit) of total consideration paid and payable in connection with the repurchase of subsidiary shares from noncontrolling interests		(74)	187
Consideration payable in connection with constructions, included in accrued liabilities		$ 1,447	$ 2,912

[1] * Dividend accrued but not paid by joint ventures of $0, $504 and $533 was included in accrued liabilities as of December 31, 2019, 2018 and 2017, respectively.