Investments in Privately-Held Raw Material Companies - Minority Investment Entities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AXT, Inc. Stockholders' Equity
Summarized income information of all the minority investment entities that are not consolidated and accounted for under the equity method [Abstract]
Net revenue	$ 5,458,000	$ 8,549,000	$ 6,152,000
Gross profit (loss)	558,000	1,675,000	482,000
Operating (loss)	(700,000)	(778,000)	(938,000)
Net (loss)	(1,876,000)	(1,080,000)	(1,694,000)
Five Minority Investments
Summarized income information of all the minority investment entities that are not consolidated and accounted for under the equity method [Abstract]
Net revenue	18,991,000	33,212,000	24,053,000
Gross profit (loss)	2,013,000	6,457,000	1,739,000
Operating (loss)	(2,266,000)	(3,152,000)	(3,676,000)
Net (loss)	(3,000,000)	(4,750,000)	(4,798,000)
Summarized balance sheet information of all the minority investment entities that are not consolidated and accounted for under the equity method [Abstract]
Current assets	22,144,000	31,525,000
Noncurrent assets	11,990,000	26,889,000
Current liabilities	13,726,000	24,670,000
Noncurrent liabilities		112,000
Minority investment entities
Entity (loss) excluding impairment	(1,900,000)	(1,100,000)	(1,700,000)
Minority Investment Entities [Member]
Minority investment entities
Dividends received	362,000	0	$ 0
Undistributed retained earnings	$ 1,200,000	$ 2,500,000