The Company and Summary of Significant Accounting Policies - Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accumulated other comprehensive income (loss):
Accumulated other comprehensive income (loss) attributable to AXT, Inc.	$ (4,862)	$ (1,972)
Accumulated other comprehensive income including noncontrolling interest
Accumulated other comprehensive income (loss):
Unrealized loss on investments, net	(3)	(84)
Cumulative translation adjustment	(4,842)	(1,845)
Accumulated other comprehensive income (loss) attributable to AXT, Inc.	(4,845)	(1,929)
Accumulated other comprehensive income attributable to noncontrolling interest
Accumulated other comprehensive income (loss):
Less: Cumulative translation adjustment attributable to noncontrolling interests	$ 17	$ 43