Document and Entity Information - USD ($)
12 Months Ended
Sep. 30, 2017
Dec. 04, 2017
Mar. 31, 2017
Document and Entity Information      
Entity Registrant Name LIQUIDITY SERVICES INC    
Entity Central Index Key 0001235468    
Document Type 10-K    
Document Period End Date Sep. 30, 2017    
Amendment Flag false    
Current Fiscal Year End Date --09-30    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Accelerated Filer    
Entity Public Float     $ 202,237,496
Entity Common Stock, Shares Outstanding   31,889,679  
Document Fiscal Year Focus 2016    
Document Fiscal Period Focus FY