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Note 15 - Stock-based Compensation (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 31, 2015	May 30, 2015	May 31, 2010
Share-based Payment Arrangement, Expense	$ 1,878,000	$ 1,778,000	$ 1,678,000
Share-based Payment Arrangement, Expense, Tax Benefit	3,918,000	1,047,000	933,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	3,960,000	$ 1,047,000	$ 933,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 3,550,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	3 years
The 2010 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	632,142					1,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized				2,575,000	1,200,000
Share-based Payment Arrangement, Option [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years