Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2012		Sep. 30, 2011	Sep. 30, 2010
Numerator:
Net income (loss) attributable to Powell Industries, Inc.	$ 11,853	$ 12,138	$ 7,411	$ (1,745)	$ (6,953)	$ 73	$ 1,733	$ 2,432	$ 29,657		$ (2,715)	$ 25,008
Denominator:
Weighted average basic shares									11,850,000		11,735,000	11,545,000
Dilutive effect of stock options, restricted stock and restricted stock units									75,000	[1]		148,000	[1]
Weighted average diluted shares with assumed conversions									11,925,000		11,735,000	11,693,000
Net earnings (loss) per share:
Basic	$ 0.99	$ 1.03	$ 0.63	$ (0.15)	$ (0.59)	$ 0.01	$ 0.15	$ 0.21	$ 2.50		$ (0.23)	$ 2.17
Diluted	$ 0.99	$ 1.02	$ 0.63	$ (0.15)	$ (0.59)	$ 0.01	$ 0.15	$ 0.21	$ 2.49		$ (0.23)	$ 2.14
Shares excluded from the computation of diluted earnings (loss) per share											23,000

[1] In fiscal year 2011, these items were excluded from diluted income (loss) per share as the effect would have been anti-dilutive.