Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 30, 2020
Document And Entity Information (Abstract)
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2020
Entity Registrant Name	Metropolitan Bank Holding Corp.
Entity File Number	001-38282
Entity Incorporation, State or Country Code	NY
Entity Tax Identification Number	13-4042724
Entity Address, Address Line One	99 Park Avenue
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10016
City Area Code	212
Local Phone Number	659-0600
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	MCB
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		8,291,264
Entity Central Index Key	0001476034
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false