Net Income Per Share (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Numerator:
Net income attributable to AXT, Inc.	$ 3,901,000	$ 1,930,000	$ 6,776,000	$ 2,595,000
Less: Preferred stock dividends	(44,000)	(44,000)	(88,000)	(88,000)
Net income available to common stockholders	$ 3,857,000	$ 1,886,000	$ 6,688,000	$ 2,507,000
Weighted-average number of common shares outstanding:
Denominator for basic net income per share - weighted-average common shares (in shares)	39,001,000	38,306,000	38,970,000	36,238,000
Effect of dilutive securities:
Denominator for dilutive net income per common share (in shares)	40,216,000	39,706,000	40,289,000	37,645,000
Net income attributable to AXT, Inc. per common share:
Basic (in dollars per share)	$ 0.10	$ 0.05	$ 0.17	$ 0.07
Diluted (in dollars per share)	$ 0.10	$ 0.05	$ 0.17	$ 0.07
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	$ 3,532,000		$ 3,532,000		$ 3,532,000
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 per share as the impact is anti-dilutive (in shares)	228,000	622,000	186,000	617,000
Restricted Stock Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from diluted net income per share as the impact is anti-dilutive (in shares)	249,000		240,000	5,000
Options
Effect of dilutive securities:
Effect of dilutive securities (in shares)	1,094,000	1,212,000	1,191,000	1,216,000
Restricted Stock Awards
Effect of dilutive securities:
Effect of dilutive securities (in shares)	121,000	188,000	128,000	191,000