Note 4 - Inventories (Details Textual) - USD ($)	3 Months Ended	9 Months Ended
Dec. 29, 2019	Dec. 28, 2019	Dec. 29, 2018	Dec. 28, 2019	Dec. 29, 2018	Mar. 31, 2019
Inventory, LIFO Reserve		$ 153,884,000	$ 160,727,000	$ 153,884,000	$ 160,727,000	$ 161,341,000
Inventory, LIFO Reserve, Period Charge	$ (11,337,000)		$ 25,776,000	(7,457,000)	15,722,000
Cost of Sales [Member]
Effect of LIFO Inventory Liquidation on Income					(39,933,000)
Discontinued Operations, Disposed of by Sale [Member] \| Modesto Facility [Member]
Effect of LIFO Inventory Liquidation on Income		$ 24,211,000		$ 24,211,000	$ 24,211,000

The effect of liquidating LIFO (last in first out) inventory layers on income.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SAB Topic 11.F)
-URI http://asc.fasb.org/extlink&oid=27011343&loc=d3e100079-122729

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Amount by which inventory stated at last-in first-out (LIFO) is less than (in excess of) inventory stated at other inventory cost methods.

+ References

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The change in the inventory reserve representing the cumulative difference in cost between the first in, first out and the last in, first out inventory valuation methods, which change has been reflected in the statement of income during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6b)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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