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Debt Intruments (narrative) (detail) (USD $)
Dec. 27, 2014
Apr. 01, 2014
Dec. 28, 2013
Debt Instruments [Abstract]      
Line of Credit Facility, Amount Outstanding $ 255,000,000us-gaap_LineOfCredit   $ 226,000,000us-gaap_LineOfCredit
Line of Credit Facility [Line Items]      
Equity Method Investments   16,308,000us-gaap_EquityMethodInvestments  
Production Period [Member]      
Line of Credit Facility [Line Items]      
Line of Credit Facility, Current Borrowing Capacity 400,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ senea_RevolverBorrowingPeriodsAxis
= senea_ProductionPeriodMember
   
Nonproduction Period [Member]      
Line of Credit Facility [Line Items]      
Line of Credit Facility, Current Borrowing Capacity $ 300,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ senea_RevolverBorrowingPeriodsAxis
= senea_NonproductionPeriodMember