Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 11, 2022	Jun. 30, 2021
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2021
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Registrant Name	Enzon Pharmaceuticals, Inc.
Entity Central Index Key	0000727510
Current Fiscal Year End Date	--12-31
Entity File Number	001-36435
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	22-2372868
Entity Address, Address Line One	20 Commerce Drive (Suite 135)
Entity Address, City or Town	Cranford
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	07016
City Area Code	732
Local Phone Number	980-4500
Title of 12(g) Security	Common Stock, $0.01 par value
Trading Symbol	ENZN
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		74,214,603
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Public Float			$ 25,051,961
ICFR Auditor Attestation Flag	false
Auditor Name	EisnerAmper LLP
Auditor Firm ID	274
Auditor Location	Philadelphia, Pennsylvania