Selected Quarterly Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Selected Quarterly Data (Unaudited) [Abstract]
Revenues	$ 28,832	$ 41,200	$ 32,783	$ 73,611	$ 54,677	$ 47,760	$ 32,944	$ 29,135	$ 176,426	$ 164,516	$ 120,308
Gross profit	$ 8,496	$ 14,599	$ 11,725	$ 20,337	$ 19,592	$ 15,502	$ 8,395	$ 8,443	55,157	51,932	34,063
Gross margin	29.50%	35.40%	35.80%	27.60%	35.80%	32.50%	25.50%	29.00%
Operating income (loss)	$ (8,848)	$ 2,936	$ 65	$ 7,766	$ 8,034	$ 3,971	$ (1,400)	$ (180)	1,919	10,425	(7,908)
Income tax provision (benefit)	370	1,390	(2,780)	1,240	474	986	194	90	220	1,744	3,100
Net (loss) income attributable to Amtech Systems, Inc.	$ (8,953)	$ 4,971	$ 2,835	$ 6,452	$ 7,317	$ 3,287	$ (1,420)	$ (53)	5,305	9,131	(7,008)
Comprehensive income (loss) attributable to Amtech Systems, Inc.									$ 3,860	$ 8,509	$ (8,749)
Net (loss) income per share attributable to Amtech Systems, Inc.:
Basic (dollars per share)	$ (0.61)	$ 0.33	$ 0.19	$ 0.44	$ 0.53	$ 0.25	$ (0.11)	$ 0.00	$ 0.36	$ 0.68	$ (0.53)
Shares used in calculation, basic	14,730	14,925	14,891	14,781	13,895	13,242	13,188	13,179	14,833	13,378	13,168
Diluted (dollars per share)	$ (0.61)	$ 0.33	$ 0.19	$ 0.42	$ 0.51	$ 0.25	$ (0.11)	$ 0.00	$ 0.35	$ 0.68	$ (0.53)
Shares used in calculation, diluted	14,730	15,091	15,154	15,298	14,294	13,398	13,188	13,179	15,065	13,501	13,168