Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended	48 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2015	Dec. 31, 2019	Oct. 27, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	$ 192,190	$ 192,762	$ 195,981	$ 194,532	$ 192,762	$ 194,532
Common stock options exercised	72	441	232
Purchase of subsidiary shares from noncontrolling interest			(413)
Reclassification out of accumulated other comprehensive income and non-controlling interest upon the deconsolidation of a subsidiary				(617)		(617)
Stock-based compensation	641	643	568	558
Net income	959	217	1,738	(1,023)	1,176	715
Net dividend declared by joint ventures	(89)
Other comprehensive income (loss)	281	(1,873)	(2,451)	2,531
Balance, end of period	194,054	192,190	195,655	195,981	194,054	195,655		$ 192,762
Reclassification adjustment from AOCI	0		0		0	0
Stock repurchase program, authorized amount									$ 5,000
Shares repurchased (in shares)							908,000	0
Average price of shares repurchased (in dollars per share)							$ 2.52
Total purchase price							$ 2,300
Stock repurchase program remaining authorized repurchase amount	2,700				2,700
Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	3,532	3,532	3,532	3,532	3,532	3,532
Balance, end of period	3,532	3,532	3,532	3,532	3,532	3,532		$ 3,532
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	41	41	40	40	41	40
Balance, end of period	41	41	40	40	41	40		41
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	238,041	236,957	234,976	234,418	236,957	234,418
Common stock options exercised	72	441	232
Purchase of subsidiary shares from noncontrolling interest			(74)
Stock-based compensation	641	643	568	558
Balance, end of period	238,754	238,041	235,702	234,976	238,754	235,702		236,957
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(47,961)	(47,783)	(46,287)	(45,183)	(47,783)	(45,183)
Net income	361	(178)	1,451	(1,104)
Balance, end of period	(47,600)	(47,961)	(44,836)	(46,287)	(47,600)	(44,836)		(47,783)
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(6,637)	(4,862)	(733)	(1,972)	(4,862)	(1,972)
Reclassification out of accumulated other comprehensive income and non-controlling interest upon the deconsolidation of a subsidiary				(1,150)
Other comprehensive income (loss)	272	(1,775)	(2,397)	2,389
Balance, end of period	(6,365)	(6,637)	(3,130)	(733)	(6,365)	(3,130)		(4,862)
AXT, Inc. Stockholders' Equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	187,016	187,885	191,528	190,835	187,885	190,835
Common stock options exercised	72	441	232
Purchase of subsidiary shares from noncontrolling interest			(74)
Reclassification out of accumulated other comprehensive income and non-controlling interest upon the deconsolidation of a subsidiary				(1,150)
Stock-based compensation	641	643	568	558
Net income	361	(178)	1,451	(1,104)
Other comprehensive income (loss)	272	(1,775)	(2,397)	2,389
Balance, end of period	188,362	187,016	191,308	191,528	188,362	191,308		187,885
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	5,174	4,877	4,453	3,697	4,877	3,697
Purchase of subsidiary shares from noncontrolling interest			(339)
Reclassification out of accumulated other comprehensive income and non-controlling interest upon the deconsolidation of a subsidiary				533
Net income	598	395	287	81
Net dividend declared by joint ventures	(89)
Other comprehensive income (loss)	9	(98)	(54)	142
Balance, end of period	$ 5,692	$ 5,174	$ 4,347	$ 4,453	$ 5,692	$ 4,347		$ 4,877