Note 9 - Earnings Per Share (Details Textual) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Percentage of Class B Common Stock Dividend or Other Distribution for Class A Common Stock Dividend or Other Distribution	0.16667%		0.16667%
Common Class A [Member]
Stock Options Excluded from Computation of Earnings Per Share, Amount		104,835		115,908
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	84,963		78,945	52,707
Common Class B [Member]
Stock Options Excluded from Computation of Earnings Per Share, Amount				19,318
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		17,473		38,784