Cover - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Dec. 07, 2020	Mar. 31, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-12488
Entity Registrant Name	Powell Industries, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	88-0106100
Entity Address, Address Line One	8550 Mosley Road
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77075-1180
City Area Code	713
Local Phone Number	944-6900
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	POWL
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 227
Entity Common Stock, Shares Outstanding		11,646,173
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement for the 2020 annual meeting of stockholders to be filed not later than 120 days after September 30, 2020, are incorporated by reference into Part III of this Form 10-K.
Amendment Flag	false
Entity Central Index Key	0000080420
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2020
Current Fiscal Year End Date	--09-30