Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income (loss) attributable to Amtech Systems, Inc.	$ 1,349	$ (1,604)	$ (2,321)	$ (5,195)	$ (3,245)	$ (5,257)	$ (3,751)	$ (794)	$ (7,771)	$ (13,047)	$ (20,069)
Weighted average shares outstanding (in shares)	13,150	13,103	11,997	9,854	9,846	9,843	9,679	9,560	12,022	9,732	9,529
Basic income (loss) per share attributable to Amtech shareholders (dollars per share)	$ 0.10	$ (0.12)	$ (0.19)	$ (0.53)	$ (0.33)	$ (0.53)	$ (0.39)	$ (0.08)	$ (0.65)	$ (1.34)	$ (2.11)
Common stock equivalents (in shares)									0	0	0	[1]
Diluted shares (in shares)	13,259	13,103	11,997	9,854	9,846	9,843	9,679	9,560	12,022	9,732	9,529
Diluted income (loss) per share attributable to Amtech shareholders (dollars per share)	$ 0.10	$ (0.12)	$ (0.19)	$ (0.53)	$ (0.33)	$ (0.53)	$ (0.39)	$ (0.08)	$ (0.65)	$ (1.34)	$ (2.11)
Stock Options and Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									1,640	1,099	1,130

[1] (1) The number of common stock equivalents is calculated using the treasury stock method and the average market price during the period.