Per Share Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Undistributed Earnings (Loss) Available to Common Shareholders, Basic									$ 40,830	$ 32,950	$ (14,113)
Noncontrolling Interest, Period Increase (Decrease)									194	0	(44)
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic									575	256	0
Comprehensive income (loss) attributable to IES Holdings, Inc.	$ 14,606	$ 12,260	$ 6,231	$ 8,502	$ 9,861	$ 10,972	$ 5,489	$ 6,884	$ 41,599	$ 33,206	$ (14,157)
Weighted Average Number of Shares Outstanding, Basic									20,795,892	21,082,012	21,196,388
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements									296,518	233,233	0
Weighted Average Number of Shares Outstanding, Diluted									21,092,410	21,315,245	21,196,388
Earnings (loss) per share, basic	$ 0.69	$ 0.58	$ 0.30	$ 0.40	$ 0.47	$ 0.52	$ 0.26	$ 0.32	$ 1.96	$ 1.56	$ (0.67)
Earnings (loss) per share, diluted	$ 0.68	$ 0.58	$ 0.29	$ 0.39	$ 0.46	$ 0.52	$ 0.26	$ 0.32	$ 1.94	$ 1.55	$ (0.67)
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount											301,879