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Note 11 (Details) (USD $)
3 Months Ended
Dec. 27, 2014
Dec. 28, 2013
Note 11 (Details) [Line Items]    
Proceeds from Sale and Maturity of Marketable Securities $ 11,601,000us-gaap_ProceedsFromSaleAndMaturityOfMarketableSecurities $ 5,495,000us-gaap_ProceedsFromSaleAndMaturityOfMarketableSecurities
Marketable Securities, Gain (Loss) (509,000)us-gaap_MarketableSecuritiesGainLoss (260,000)us-gaap_MarketableSecuritiesGainLoss
Mutual Funds [Member]    
Note 11 (Details) [Line Items]    
Unrealized Gain (Loss) on Securities (3,700,000)us-gaap_UnrealizedGainLossOnSecurities
/ us-gaap_InvestmentTypeAxis
= jjsf_MutualFundsMember
 
Marketable Securities $ 94,300,000us-gaap_MarketableSecurities
/ us-gaap_InvestmentTypeAxis
= jjsf_MutualFundsMember