Other income (expense), net (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Other income (expense), net
Foreign exchange gain (loss)	$ 1,573,000	$ (434,000)	$ (411,000)
Income from local China government subsidy	1,710,000	1,125,000	3,800,000
Other income (expense)	204,000	(182,000)	(189,000)
Total other income, net	$ 3,487,000	$ 509,000	$ 3,200,000