Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Basic Income (Loss) Per Share Computation
Net income (loss) attributable to Amtech Systems, Inc.	$ 2,835	$ (1,420)	$ 9,287	$ (1,475)
Weighted Average Shares Outstanding:
Common stock (in shares)	14,891	13,188	14,835	13,184
Basic income (loss) per share attributable to Amtech shareholders (USD per share)	$ 0.19	$ (0.11)	$ 0.63	$ (0.11)
Diluted Income (Loss) Per Share Computation
Net income (loss) attributable to Amtech Systems, Inc.	$ 2,835	$ (1,420)	$ 9,287	$ (1,475)
Weighted Average Shares Outstanding:
Common stock (in shares)	14,891	13,188	14,835	13,184
Common stock equivalents (in shares)	263	0	388	0
Diluted shares (in shares)	15,154	13,188	15,223	13,184
Diluted income (loss) per share attributable to Amtech shareholders (USD per share)	$ 0.19	$ (0.11)	$ 0.61	$ (0.11)
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	422	1,669	296	1,696