Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic Income Per Share Computation
Net income attributable to Amtech Systems, Inc.	$ 4,971	$ 3,287	$ 14,258	$ 1,812
Weighted Average Shares Outstanding:
Common stock (in shares)	14,925	13,242	14,867	13,203
Basic income per share attributable to Amtech shareholders (USD per share)	$ 0.33	$ 0.25	$ 0.96	$ 0.14
Diluted Income Per Share Computation
Net income attributable to Amtech Systems, Inc.	$ 4,971	$ 3,287	$ 14,258	$ 1,812
Weighted Average Shares Outstanding:
Common stock (in shares)	14,925	13,242	14,867	13,203
Common stock equivalents (in shares)	166	156	314	85
Diluted shares (in shares)	15,091	13,398	15,181	13,288
Diluted income per share attributable to Amtech shareholders (USD per share)	$ 0.33	$ 0.25	$ 0.94	$ 0.14
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	679	1,152	428	1,649