Stockholders' Equity and Stock Repurchase Program - Ownership Interest in Consolidated Subsidiaries (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stockholders’ Equity and Stock Repurchase Program
Net income (loss) attributable to AXT, Inc.	$ (2,049)	$ (898)	$ 1,451	$ (1,104)	$ (1,061)	$ 3,939	$ 3,901	$ 2,875	$ (2,600)	$ 9,654	$ 10,148
Increase (decrease) in paid-in capital for:
Purchase of subsidiary shares from noncontrolling interest									(74)	187
Net transfers to noncontrolling interests									(74)	187
Net income (loss) attributable to AXT, Inc., net of transfers to noncontrolling interests									$ (2,674)	$ 9,841