Unaudited Quarterly Consolidated Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unaudited Quarterly Consolidated Financial Data
Revenue	$ 27,035	$ 25,469	$ 22,134	$ 20,723	$ 18,410	$ 19,841	$ 24,797	$ 20,208	$ 95,361	$ 83,256	$ 102,397
Gross profit	9,162	8,823	6,768	5,522	3,865	5,759	8,506	6,695	30,275	24,825	37,047
Net income (loss) attributable to AXT, Inc	$ 2,064	$ 991	$ 361	$ (178)	$ (2,049)	$ (898)	$ 1,451	$ (1,104)	$ 3,238	$ (2,600)	$ 9,654
Net income (loss) attributable to AXT, Inc. per share, basic (in dollar per share)	$ 0.05	$ 0.02	$ 0.01	$ (0.01)	$ (0.05)	$ (0.02)	$ 0.04	$ (0.03)	$ 0.08	$ (0.07)	$ 0.24
Net income (loss) attributable to AXT, Inc. per share, diluted (in dollar per share)	$ 0.05	$ 0.02	$ 0.01	$ (0.01)	$ (0.05)	$ (0.02)	$ 0.04	$ (0.03)	$ 0.07	$ (0.07)	$ 0.24