Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2023	Feb. 29, 2024	Jun. 30, 2023
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Document Transition Report	false
Entity File Number	001-36576
Entity Registrant Name	Marinus Pharmaceuticals, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-0198082
Entity Address, Address Line One	5 Radnor Corporate Center, Suite 500
Entity Address, Address Line Two	100 Matsonford Road
Entity Address, City or Town	Radnor
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19087
City Area Code	484
Local Phone Number	801-4670
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	MRNS
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	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 545,158,729
Entity Common Stock, Shares Outstanding		54,642,580
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	Philadelphia, Pennsylvania
Entity Central Index Key	0001267813
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false