Document And Entity Information - shares	9 Months Ended
	Dec. 26, 2020	Jan. 22, 2021
Document Information [Line Items]
Entity Central Index Key	0000088948
Entity Registrant Name	Seneca Foods Corporation
Amendment Flag	false
Current Fiscal Year End Date	--03-31
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2021
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Dec. 26, 2020
Document Transition Report	false
Entity File Number	0-01989
Entity Incorporation, State or Country Code	NY
Entity Tax Identification Number	16-0733425
Entity Address, Address Line One	3736 South Main Street
Entity Address, City or Town	Marion
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	14505
City Area Code	315
Local Phone Number	926-8100
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Common Class B [Member]
Document Information [Line Items]
Title of 12(b) Security	Common Stock Class B, $.25 Par
Trading Symbol	SENEB
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		1,718,002
Common Class A [Member]
Document Information [Line Items]
Title of 12(b) Security	Common Stock Class A, $.25 Par
Trading Symbol	SENEA
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		7,350,186