Net Income (Loss) per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Numerator:
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
Less: Preferred stock dividends									(177)	(177)	(177)
Net income (loss) available to common stockholders									$ 3,061	$ (2,777)	$ 9,477
Denominator:
Denominator for basic net income (loss) per share - weighted-average common shares									40,152	39,487	39,049
Effect of dilutive securities:
Denominator for dilutive net income (loss) per common shares									41,025	39,487	40,265
Basic net income per share:
Net income (loss) to common stockholders	$ 0.05	$ 0.02	$ 0.01	$ (0.01)	$ (0.05)	$ (0.02)	$ 0.04	$ (0.03)	$ 0.08	$ (0.07)	$ 0.24
Diluted net income per share:
Net income (loss) to common stockholders	$ 0.05	$ 0.02	$ 0.01	$ (0.01)	$ (0.05)	$ (0.02)	$ 0.04	$ (0.03)	$ 0.07	$ (0.07)	$ 0.24
Options
Effect of dilutive securities:
Effect of dilutive securities (in shares)									602		1,106
Weighted-average shares:
Securities excluded from diluted net income (loss) per share as the impact is anti-dilutive (in shares)									862	2,953	266
Restricted Stock Awards
Effect of dilutive securities:
Effect of dilutive securities (in shares)									271		110
Weighted-average shares:
Securities excluded from diluted net income (loss) per share as the impact is anti-dilutive (in shares)									161	939	227