Selected Quarterly Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Selected Quarterly Data (Unaudited) [Abstract]
Revenue	$ 54,677	$ 47,760	$ 32,944	$ 29,135	$ 42,409	$ 33,342	$ 22,483	$ 22,074	$ 164,516	$ 120,308	$ 104,883
Gross profit	19,592	15,502	8,395	8,443	12,476	9,631	6,001	5,955	51,932	34,063	27,008
Provision for income taxes	474	986	194	90	1,060	70	1,670	300	1,744	3,100	1,910
Net loss attributable to Amtech Systems, Inc.	$ 7,317	$ 3,287	$ (1,420)	$ (53)	$ (285)	$ (1,209)	$ (1,499)	$ (4,015)	9,131	(7,008)	(7,771)
Comprehensive income (loss) attributable to Amtech Systems, Inc.									$ 8,509	$ (8,749)	$ (9,727)
Net loss per share attributable to Amtech Systems, Inc.:
Basic (dollars per share)	$ 0.53	$ 0.25	$ (0.11)	$ 0.00	$ (0.02)	$ (0.09)	$ (0.11)	$ (0.31)	$ 0.68	$ (0.53)	$ (0.65)
Shares used in calculation, basic	13,895	13,242	13,188	13,179	13,177	13,173	13,169	13,152	13,378	13,168	12,022
Diluted (dollars per share)	$ 0.51	$ 0.25	$ (0.11)	$ 0.00	$ (0.02)	$ (0.09)	$ (0.11)	$ (0.31)	$ 0.68	$ (0.53)	$ (0.65)
Shares used in calculation, diluted	14,294	13,398	13,188	13,179	13,177	13,173	13,169	13,152	13,501	13,168	12,022