Quarterly Results Of Operations (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Results Of Operations (Unaudited) [Abstract]
Revenues	$ 240,275	$ 232,576	$ 205,677	$ 198,300	$ 206,581	$ 208,323	$ 203,662	$ 192,178	$ 876,828	$ 810,744	$ 695,993
Gross Profit	40,521	42,537	33,840	33,064	38,104	35,398	31,814	35,182	149,962	140,498	126,980
Net Income Attributable to IES Holdings	$ 4,675	$ 8,516	$ 2,221	$ (29,569)	$ 3,146	$ 5,868	$ 536	$ 3,872	$ (14,157)	$ 13,422	$ 120,778
Earnings Per Share, Basic	$ 0.22	$ 0.4	$ 0.11	$ (1.39)	$ 0.15	$ 0.27	$ 0.02	$ 0.18	$ (0.67)	$ 0.62	$ 5.63
Earnings Per Share, Diluted	$ 0.22	$ 0.4	$ 0.11	$ (1.39)	$ 0.14	$ 0.27	$ 0.02	$ 0.18	$ (0.67)	$ 0.62	$ 5.62