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Document and Entity Information (USD $)
 12 Months Ended
Mar. 31, 2012
Oct. 01, 2011
May 26, 2012
Common Class A Member
May 26, 2012
Common Class B Member
Document And Entity Information [Abstract]        
Document Type 10-K      
Document period end date Mar. 31, 2012      
Amendment flag false      
Document Period Focus FY      
Document Fiscal Year Focus 2012      
Current fiscal year end date --03-31      
Entity central index key 0000088948      
Entity current reporting status Yes      
Entity filer category Accelerated Filer      
Entity registrant name SENECA FOODS CORP /NY/      
Entity voluntary filers No      
Entity well known seasoned issuer No      
Class Of Stock [Line Items]        
Entity common stock shares outstanding     9,595,437 2,097,312
Entity public float   $ 194,707,000