Note 2 - Earnings Per Common Share (Details Textual)			3 Months Ended		6 Months Ended
	Aug. 13, 2020	Jul. 07, 2017	Jun. 30, 2020 shares	Jun. 30, 2019 shares	Jun. 30, 2020 shares	Jun. 30, 2019 shares
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)			187,300	317,800	200,900	317,800
Unvested Performance Unit Awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)			66,658	72,796	66,658	72,796
Stock Split from [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio		5
Stock Split from [Member] | Forecast [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	3
Stock Split To [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio		3
Stock Split To [Member] | Forecast [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	2