Note 7 - Long-term Debt - Credit Agreement (Details) - Revolving Credit Facility [Member]	12 Months Ended
	Dec. 31, 2020
Average Excess Revolver Availability of $25,000,000 or More [Member] | Eurodollar [Member]
Rate	1.00%
Average Excess Revolver Availability of $25,000,000 or More [Member] | Domestic Rate [Member]
Rate	0.50%
Average Excess Revolver Availability of $17,500,000 to Less Than 25,000,000 [Member] | Eurodollar [Member]
Rate	1.25%
Average Excess Revolver Availability of $17,500,000 to Less Than 25,000,000 [Member] | Domestic Rate [Member]
Rate	0.50%
Average Excess Revolver Availability of $10,000,000 to Less Than 17,500,000 [Member] | Eurodollar [Member]
Rate	1.50%
Average Excess Revolver Availability of $10,000,000 to Less Than 17,500,000 [Member] | Domestic Rate [Member]
Rate	2.50%
Average Excess Revolver Availability of Less Than $10,000,000 [Member] | Eurodollar [Member]
Rate	1.75%
Average Excess Revolver Availability of Less Than $10,000,000 [Member] | Domestic Rate [Member]
Rate	0.00%