Note 7 - Inventories (Details Textual) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Inventory, LIFO Reserve, Period Charge	$ 400	$ 1,400	$ 3,340	$ 6,615
Inventory Write-down	$ 8,400	$ 3,100	$ 14,700	$ 8,400

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.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration