Quarterly Results of Operations (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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 330,411	$ 293,125	$ 291,277	$ 276,043	$ 293,607	$ 282,633	$ 256,914	$ 243,842	$ 1,190,856	$ 1,076,996	$ 876,828
Gross profit	68,160	58,320	51,264	50,215	50,870	46,397	43,235	41,601	227,959	182,103	149,962
Net 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)
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)
Goodwill impairment expense	$ 6,976								$ 6,976	$ 0	$ 0