COVER PAGE - USD ($) $ in Billions	12 Months Ended
COVER PAGE - USD ($) $ in Billions	Dec. 31, 2020	Feb. 23, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K/A
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	000-50194
Entity Registrant Name	HMS HOLDINGS CORP
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	5615 High Point Drive
Entity Address, City or Town	Irving
Entity Address, State or Province	TX
Entity Tax Identification Number	11-3656261
Entity Address, Postal Zip Code	75038
City Area Code	214
Local Phone Number	453-3000
Title of 12(b) Security	Common Stock $0.01 par value
Trading Symbol	HMSY
Security Exchange Name	NASDAQ
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			$ 1.8
Common Stock, Shares Outstanding (in shares)		88,638,966
Documents Incorporated by Reference	None.
Amendment Description	This Amendment No. 1 to the Annual Report on Form 10-K/A (this "Amendment") amends the Registrant's Annual Report on Form 10-K for the year ended December 31, 2020 (the "Annual Report"), as filed by the Registrant with the Securities and Exchange Commission ("SEC") on February 26, 2021 (the "Original Filing"), and is being filed solely to replace Part III, Items 10 through Item 14 and to include additional exhibits to the Exhibit Index referenced in Item 15 of the Original Filing, which includes the Certifications to this Amendment. The reference in the Original Filing to the incorporation by reference of the Registrant's definitive proxy statement into Part III of the Annual Report on Form 10-K is hereby deleted.For purposes of this Amendment, and in accordance with Rule 12b-15 under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), (i) Items 10 through 14 in the Original Filing have been amended and restated in their entirety, (ii) the Exhibit Index in the Original Filing has been amended to include the new exhibits set forth herein and (iii) the reference on the cover of the Original Filing to the incorporation by reference to portions of our definitive proxy statement into Part III of the Original Filing has been deleted. Except as specifically provided herein, this Amendment does not reflect events occurring after the filing of the Original Filing and no attempt has been made in this Amendment to modify or update other disclosures as presented in the Original Filing. Accordingly, this Amendment should be read in conjunction with the Original Filing and any filings with the SEC made thereafter.
Entity Central Index Key	0001196501
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	true
ICFR Auditor Attestation Flag	true

HMS HOLDINGS CORP 10-K/A