CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income (loss)		$ 5,041,000	$ (1,588,000)	$ 11,009,000
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization		4,333,000	5,531,000	4,871,000
Amortization of marketable securities premium		34,000	37,000	158,000
Impairment charge on equity investee			1,068,000
Stock-based compensation		2,623,000	2,346,000	1,925,000
Provision for doubtful accounts		183,000
(Gain) loss on disposal of equipment		50,000	72,000	(99,000)
Gain from deconsolidation of a subsidiary			(175,000)
(Gain) loss from equity method investments, net		(111,000)	983,000	1,080,000
Return on equity method investments			362,000
Changes in operating assets and liabilities:
Accounts receivable		(5,333,000)	441,000	2,819,000
Inventories		(916,000)	8,862,000	(14,629,000)
Prepaid expenses and other current assets		(6,719,000)	2,936,000	(4,600,000)
Other assets		(104,000)	(1,188,000)	(1,888,000)
Accounts payable		2,305,000	(3,137,000)	2,314,000
Accrued liabilities	[1]	2,601,000	(4,010,000)	518,000
Other long-term liabilities, including royalties		1,878,000	118,000	(260,000)
Net cash provided by operating activities		5,865,000	12,658,000	3,218,000
Cash flows from investing activities:
Purchases of property, plant and equipment		(19,855,000)	(21,792,000)	(40,539,000)
Proceeds from sale of equipment				99,000
Purchases of available-for-sale debt securities		(5,968,000)	(8,725,000)	(9,937,000)
Proceeds from sales and maturities of available-for-sale debt securities		9,401,000	22,189,000	19,550,000
Net cash used in investing activities		(16,422,000)	(8,328,000)	(30,827,000)
Cash flows from financing activities:
Proceeds from common stock options exercised		2,536,000	268,000	628,000
Proceeds from sale of previously consolidated subsidiary shares			366,000
Consideration paid to repurchase subsidiary shares from noncontrolling interests			(262,000)	(415,000)
Proceeds from short-term loan		10,401,000	5,814,000
Payments on short-term loan		(5,996,000)
Proceeds from sale of subsidiary shares to noncontrolling interest		396,000
Proceeds from issuance of Tongmei's common stock to redeemable noncontrolling interests net of issuance cost		47,563,000
Dividends paid by joint ventures to their minority shareholders		(2,238,000)
Net cash provided by (used in) financing activities		52,662,000	6,186,000	213,000
Effect of exchange rate changes on cash and cash equivalents		3,605,000	(150,000)	(430,000)
Net increase (decrease) in cash and cash equivalents		45,710,000	10,366,000	(27,826,000)
Cash and cash equivalents at the beginning of the year		26,892,000	16,526,000	44,352,000
Cash and cash equivalents at the end of the year		72,602,000	26,892,000	16,526,000
Supplemental disclosures:
Income taxes paid, net of refunds		1,959,000	749,000	1,134,000
Supplemental disclosure of non-cash flow information:
Consideration payable to repurchase subsidiary shares from noncontrolling interests, included in accrued liabilities		1,439,000	151,000	1,192,000
Reduction of noncontrolling interests in excess (deficit) of total consideration paid and payable in connection with the repurchase of subsidiary shares from noncontrolling interests		(1,398,000)	(74,000)	187,000
Consideration payable in connection with construction, included in accrued liabilities		$ 1,457,000	$ 1,447,000	$ 2,912,000

[1] * Dividend accrued but not paid by joint ventures of $0, $0 and $504 was included in accrued liabilities as of December 31, 2020, 2019 and 2018, respectively.