Stockholders' Equity (Details) - USD ($)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Oct. 27, 2014	Feb. 21, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period				$ 144,688,000
Common stock options exercised				165,000
Common stock repurchased				(2,254,000)
Stock-based compensation				1,051,000
Net (loss) income	$ 47,000	$ 870,000	$ 870,000	(728,000)	$ (404,000)
Dividends declared by joint ventures				(83,000)
Change in unrealized (loss) gain on marketable securities	(134,000)	(418,000)		(484,000)	(279,000)
Currency translation adjustment				(2,321,000)
Balance, end of period	$ 140,034,000	144,688,000		140,034,000		$ 144,688,000
Reclassification adjustment from AOCI				$ 0	$ 0
Stock Repurchase Program [Abstract]
Stock repurchase program, authorized amount								$ 5,000,000	$ 6,000,000
Shares repurchased (in shares)	308,000			891,000		0	285,000
Average price of shares repurchased (in dollars per share)	$ 2.38			$ 2.53			$ 2.51
Total purchase price	$ 733,000			$ 2,300,000			$ 716,000
Stock repurchase program remaining authorized repurchase amount	2,700,000			2,700,000			$ 5,300,000
Preferred Stock [Member]
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		$ 3,532,000
Common Stock [Member]
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		32,000
Additional Paid In Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period				195,419,000
Common stock options exercised				165,000
Common stock repurchased				(2,254,000)
Stock-based compensation				1,051,000
Balance, end of period	194,381,000	195,419,000		194,381,000		195,419,000
Accumulated Deficit [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period				(68,393,000)
Net (loss) income				(985,000)
Balance, end of period	(69,378,000)	(68,393,000)		(69,378,000)		(68,393,000)
Other Comprehensive Income/(Loss) [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period				7,673,000
Change in unrealized (loss) gain on marketable securities				(484,000)
Currency translation adjustment				(2,023,000)
Balance, end of period	5,166,000	7,673,000		5,166,000		7,673,000
AXT, Inc. Stockholders' Equity [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period				138,263,000
Common stock options exercised				165,000
Common stock repurchased				(2,254,000)
Stock-based compensation				1,051,000
Net (loss) income				(985,000)
Dividends declared by joint ventures				0
Change in unrealized (loss) gain on marketable securities				(484,000)
Currency translation adjustment				(2,023,000)
Balance, end of period	133,733,000	138,263,000		133,733,000		138,263,000
Noncontrolling Interests [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period				6,425,000
Net (loss) income				257,000
Dividends declared by joint ventures				(83,000)
Currency translation adjustment				(298,000)
Balance, end of period	$ 6,301,000	$ 6,425,000		$ 6,301,000		$ 6,425,000