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Document and Entity Information - USD ($)
 12 Months Ended
Mar. 31, 2016
May. 27, 2016
Sep. 30, 2015
Document And Entity Information      
Entity Registrant Name 8X8 INC /DE/    
Entity Central Index Key 0001023731    
Document Type 10-K    
Document Period End Date Mar. 31, 2016    
Amendment Flag false    
Current Fiscal Year End Date --03-31    
Is Entity a Well-known Seasoned Issuer? Yes    
Is Entity a Voluntary Filer? No    
Is Entity's Reporting Status Current? Yes    
Entity Filer Category Large Accelerated Filer    
Entity Public Float     $ 715,364,941
Entity Common Stock, Shares Outstanding   89,370,746  
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2016