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Significant Accounting Policies (narrative) (detail) (USD $)	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Sales Revenue [Line Items]
Net Sales	$ 1,286,350,000us-gaap_SalesRevenueNet	$ 1,340,208,000us-gaap_SalesRevenueNet	$ 1,276,297,000us-gaap_SalesRevenueNet
Advertising Expense	1,700,000us-gaap_AdvertisingExpense	1,500,000us-gaap_AdvertisingExpense	1,400,000us-gaap_AdvertisingExpense
Deferred Financing Cost	500,000us-gaap_DeferredFinanceCostsCurrentGross
General Mills Operations LLC [Member]
Sales Revenue [Line Items]
Net Sales	138,600,000us-gaap_SalesRevenueNet / us-gaap_MajorCustomersAxis = senea_GeneralMillsOperationsLlcMember	150,300,000us-gaap_SalesRevenueNet / us-gaap_MajorCustomersAxis = senea_GeneralMillsOperationsLlcMember
UnshippedProduct	$ 60,500,000senea_Unshippedproduct / us-gaap_MajorCustomersAxis = senea_GeneralMillsOperationsLlcMember
Net Sales Percentage	13.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_MajorCustomersAxis = senea_GeneralMillsOperationsLlcMember	13.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_MajorCustomersAxis = senea_GeneralMillsOperationsLlcMember	13.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_MajorCustomersAxis = senea_GeneralMillsOperationsLlcMember
Top Ten Customers [Member]
Sales Revenue [Line Items]
Net Sales Percentage	49.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_MajorCustomersAxis = senea_TopTenCustomersMember	50.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_MajorCustomersAxis = senea_TopTenCustomersMember	47.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_MajorCustomersAxis = senea_TopTenCustomersMember
Seneca Foods Plants [Member]
Real Estate Properties [Line Items]
Number of Real Estate Properties	24us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = senea_SenecaFoodsPlantsMember
Seneca Foods Warehouses [Member]
Real Estate Properties [Line Items]
Number of Real Estate Properties	30us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = senea_SenecaFoodsWarehousesMember

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