Stockholders' Equity and Stock Repurchase Program - Ownership Interest in Consolidated Subsidiaries (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stockholders' Equity and Stock Repurchase Program
Net income (loss) attributable to AXT, Inc	$ 2,064	$ 991	$ 361	$ (178)	$ (2,049)	$ (898)	$ 1,451	$ (1,104)	$ 3,238	$ (2,600)	$ 9,654
Increase (decrease) in additional paid-in capital for:
Sales of subsidiary shares to noncontrolling interest									396
Purchase of subsidiary shares from noncontrolling interest									(1,398)	(74)
Adjustment to noncontrolling interests in connection with the reorganization and alignment of assets under Tongmei									(10,732)
Net transfers to noncontrolling interests									(11,734)	(74)
Change from net income (loss) attributable to AXT, Inc., net of transfers to noncontrolling interest									$ (8,496)	$ (2,674)