Note 5 - Share Repurchase Program (Details Textual)		3 Months Ended	12 Months Ended
	Jul. 07, 2017	Mar. 31, 2020 USD ($) shares	Dec. 31, 2019 shares	Aug. 31, 2019 USD ($) 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		1,800,000		1,800,000	3,300,000	2,000,000	1,000,000
Stock Repurchase Program, Authorized Amount		$ 33,400,000		$ 34,000,000		$ 40,000,000
Stock Repurchased and Retired During Period, Shares (in shares) | shares		35,376	0
Stock Repurchased and Retired During Period, Value		$ 597,000
Additional Paid-in Capital [Member]
Stock Repurchased and Retired During Period, Value		$ 596,000
Stock Split from [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	5
Stock Split To [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	3