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Note 8 - Share Repurchase Program (Details Textual)			3 Months Ended		12 Months Ended
	Aug. 13, 2020	Jul. 07, 2017	Mar. 31, 2020 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 shares	Dec. 31, 2018 USD ($)	Aug. 31, 2020 shares	Aug. 31, 2019 USD ($) shares	Aug. 15, 2017 shares	Nov. 04, 2015 USD ($) shares	Dec. 31, 2007 shares
Stock Repurchase Program, Number of Shares Authorized to be Repurchased (in shares) | shares								2,700,000	1,800,000	3,300,000	2,000,000	1,000,000
Stock Repurchase Program, Authorized Amount | $									$ 34,000,000		$ 40,000,000
Stock Repurchased and Retired During Period, Shares (in shares) | shares			53,064	300,000		0
Stock Repurchased and Retired During Period, Value | $			$ 597,000	$ 3,800,000	$ 597,000		$ 3,756,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount | $					$ 33,400,000
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased (in shares) | shares					2,600,000
Stock Split To [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	3	5
Stock Split from [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	2	3

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Amount of stock repurchase plan authorized.

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The number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

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Amount remaining of a stock repurchase plan authorized.

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The remaining number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

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Number of shares that have been repurchased and retired during the period.

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Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

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Ratio applied to the conversion of stock split, for example but not limited to, one share converted to two or two shares converted to one.

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