Document And Entity Information - USD ($)
12 Months Ended
Sep. 30, 2016
Dec. 28, 2016
Mar. 31, 2016
Document And Entity Information [Abstract]      
Entity Registrant Name Oncobiologics, Inc.    
Entity Central Index Key 0001649989    
Trading Symbol ons    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Current Fiscal Year End Date --09-30    
Entity Filer Category Smaller Reporting Company    
Entity Well-known Seasoned Issuer No    
Entity Common Stock, Shares Outstanding   23,578,942  
Entity Public Float     $ 0
Document Type 10-K    
Document Period End Date Sep. 30, 2016    
Amendment Flag false    
Document Fiscal Year Focus 2016    
Document Fiscal Period Focus FY