Net Income (Loss) per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income (loss) attributable to AXT, Inc.	$ (2,049)	$ (898)	$ 1,451	$ (1,104)	$ (1,061)	$ 3,939	$ 3,901	$ 2,875	$ (2,600)	$ 9,654	$ 10,148
Less: Preferred stock dividends									(177)	(177)	(177)
Net income (loss) available to common stockholders									$ (2,777)	$ 9,477	$ 9,971
Denominator:
Denominator for basic net income (loss) per share - weighted-average common shares									39,487	39,049	37,444
Effect of dilutive securities:
Denominator for dilutive net income (loss) per common shares									39,487	40,265	38,966
Basic net income per share:
Net income (loss) attributable to AXT, Inc.									$ (0.07)	$ 0.24	$ 0.27
Net income (loss) to common stockholders	$ (0.05)	$ (0.02)	$ 0.04	$ (0.03)	$ (0.03)	$ 0.10	$ 0.10	$ 0.07	(0.07)	0.24	0.27
Diluted net income per share:
Net income (loss) attributable to AXT, Inc.									(0.07)	0.24	0.26
Net income (loss) to common stockholders	$ (0.05)	$ (0.02)	$ 0.04	$ (0.03)	$ (0.03)	$ 0.10	$ 0.10	$ 0.07	$ (0.07)	$ 0.24	$ 0.26
Options
Effect of dilutive securities:
Effect of dilutive securities (in shares)										1,106	1,339
Weighted-average shares:
Securities excluded from diluted net income (loss) per share as the impact is anti-dilutive (in shares)									2,953	266	86
Restricted Stock Awards
Effect of dilutive securities:
Effect of dilutive securities (in shares)										110	183
Weighted-average shares:
Securities excluded from diluted net income (loss) per share as the impact is anti-dilutive (in shares)									939	227	63