Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Numerator:
Net loss attributable to AXT, Inc.	$ 361	$ 1,451	$ 183	$ 347
Less: Preferred stock dividends	(44)	(44)	(88)	(88)
Net loss available to common stockholders	$ 317	$ 1,407	$ 95	$ 259
Weighted-average number of common shares outstanding:
Denominator for basic net loss per share - weighted-average common shares	39,973,000	39,447,000	39,891,000	39,399,000
Effect of dilutive securities:
Denominator for dilutive net loss per common shares	40,750,000	40,123,000	40,543,000	40,045,000
Net loss attributable to AXT, Inc. per common share:
Basic	$ 0.01	$ 0.04	$ 0.00	$ 0.01
Diluted	$ 0.01	$ 0.04	$ 0.00	$ 0.01
Preferred stock, shares issued (in shares)	883,000		883,000		883,000
Preferred stock, shares outstanding (in shares)	883,000		883,000		883,000
Preferred stock, par value (in dollars per share)	$ 0.001		$ 0.001		$ 0.001
Preferred stock, value	$ 3,532		$ 3,532		$ 3,532
Cumulative annual dividend rate (as a percent)			5.00%		5.00%
Liquidation preference over common stock (in dollars per share)	$ 4		$ 4		$ 4
Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from diluted net income (loss) per share as the impact is anti-dilutive (in shares)	1,270,000	1,280,000	1,701,000	1,284,000
Restricted Stock Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from diluted net income (loss) per share as the impact is anti-dilutive (in shares)	343,000	568,000	436,000	550,000
Options
Effect of dilutive securities:
Effect of dilutive securities (in shares)	552,000	624,000	478,000	602,000
Restricted Stock Awards
Effect of dilutive securities:
Effect of dilutive securities (in shares)	225,000	52,000	174,000	44,000