Stockholders' Equity (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Oct. 27, 2014	Feb. 21, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			$ 137,561,000
Common stock options exercised			428,000
Stock-based compensation			789,000
Net (loss) income	$ 2,211,000	$ 47,000	2,942,000	$ (728,000)
Dividends declared by joint ventures			(52,000)
Other comprehensive income	(345,000)	$ (2,760,000)	(2,054,000)	(2,805,000)
Balance, end of period	139,614,000		139,614,000		$ 137,561,000
Reclassification adjustment from AOCI			0	$ 0
Stock repurchase program, authorized amount								$ 5,000,000	$ 6,000,000
Shares repurchased (in shares)					908,000	0	285,000
Average price of shares repurchased (in dollars per share)					$ 2.52		$ 2.51
Total purchase price					$ 2,300,000		$ 716,000
Stock repurchase program remaining authorized repurchase amount	2,700,000		2,700,000				$ 5,300,000
Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			3,532,000
Common stock options exercised
Balance, end of period	3,532,000		3,532,000		3,532,000
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			32,000
Common stock options exercised
Balance, end of period	32,000		32,000		32,000
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			194,646,000
Common stock options exercised			428,000
Stock-based compensation			789,000
Balance, end of period	195,863,000		195,863,000		194,646,000
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			(70,621,000)
Net (loss) income			3,422,000
Balance, end of period	(67,199,000)		(67,199,000)		(70,621,000)
Accumulated Other Comprehensive Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			4,382,000
Other comprehensive income			(1,853,000)
Balance, end of period	2,529,000		2,529,000		4,382,000
AXT, Inc. Stockholders' Equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			131,971,000
Common stock options exercised			428,000
Stock-based compensation			789,000
Net (loss) income			3,422,000
Other comprehensive income			(1,853,000)
Balance, end of period	134,757,000		134,757,000		131,971,000
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period			5,590,000
Net (loss) income			(480,000)
Dividends declared by joint ventures			(52,000)
Other comprehensive income			(201,000)
Balance, end of period	$ 4,857,000		$ 4,857,000		$ 5,590,000