Cover Page - USD ($)	12 Months Ended
	Sep. 30, 2019	Nov. 19, 2019	Mar. 29, 2019
Cover page.
Document Type	10-K
Document Annual Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	1-12997
Entity Registrant Name	MAXIMUS, INC
Entity Incorporation, State or Country Code	VA
Entity Tax Identification Number	54-1000588
Entity Address, Address Line One	1891 Metro Center Drive
Entity Address, City or Town	Reston
Entity Address, State or Province	VA
Entity Address, Postal Zip Code	20190
City Area Code	703
Local Phone Number	251-8500
Title of 12(b) Security	Common Stock, no par value
Trading Symbol	MMS
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 4,470,336,229
Entity Common Stock, Shares Outstanding		63,979,497
Documents Incorporated by Reference	Portions of the registrant's definitive Proxy Statement for its 2020 Annual Meeting of Shareholders to be held on March 17, 2020, which definitive Proxy Statement will be filed with the Securities and Exchange Commission not later than 120 days after the end of the registrant's fiscal year, are incorporated by reference into Part III of this Form 10-K.
Entity Central Index Key	0001032220
Amendment Flag	false
Current Fiscal Year End Date	--09-30
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY