Note 8 - Credit Agreement (Details) - Wells Fargo Preferred Capital, Inc. - USD ($)	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Line of Credit Facility, Initiation Date	Sep. 11, 2009
Line of Credit Facility, Description	Company entered into a credit facility with Wells Fargo Preferred Capital, Inc. (now Wells Fargo Bank, N.A.).
Line of Credit Facility, Current Borrowing Capacity	$ 102.8	$ 87.7
Line of Credit Facility, Interest Rate at Period End	3.50%	4.45%