Net Income Per Share (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Numerator:
Net income attributable to AXT, Inc.	$ 2,875,000	$ 665,000
Less: Preferred stock dividends	(44,000)	(44,000)
Net income available to common stockholders	$ 2,831,000	$ 621,000
Weighted-average number of common shares outstanding:
Denominator for basic net income per share - weighted-average common shares (in shares)	38,941,000	34,210,000
Effect of dilutive securities:
Denominator for dilutive net income per common share (in shares)	40,364,000	35,624,000
Net income attributable to AXT, Inc. per common share:
Basic (in dollars per share)	$ 0.07	$ 0.02
Diluted (in dollars per share)	$ 0.07	$ 0.02
Preferred stock, shares issued (in shares)	883,000		883,000
Preferred stock, shares outstanding (in shares)	883,000		883,000
Preferred stock, par value (in dollars per share)	$ 0.001		$ 0.001
Preferred stock, value	$ 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
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)	184,000	639,000
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)	240,000
Options
Effect of dilutive securities:
Effect of dilutive securities (in shares)	1,289,000	1,220,000
Restricted Stock Awards
Effect of dilutive securities:
Effect of dilutive securities (in shares)	134,000	194,000