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Document and Entity Information - USD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2018
Dec. 15, 2018
Mar. 31, 2018
Entity Registrant Name Magyar Bancorp, Inc.    
Entity Central Index Key 0001337068    
Document Type 10-K    
Document Period End Date Sep. 30, 2018    
Amendment Flag false    
Current Fiscal Year End Date --09-30    
Is Entity a Well-known Seasoned Issuer? No    
Is Entity a Voluntary Filer? No    
Is Entity's Reporting Status Current? Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business true    
Entity Shell Company false    
Entity Emerging Growth Company false    
Entity Public Float     $ 33,400
Entity Common Stock, Shares Outstanding   5,820,746  
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2018    
Magyar Bancorp, MHC [Member]      
Entity Common Stock, Shares Owned by Registrant's mutual holding company   3,200,450