Note 7 - Earnings Per Share (Details Textual)	3 Months Ended
	Mar. 31, 2017 shares	Mar. 31, 2016 shares
Common Class A [Member]
Common Stock to Dividend or Distribution Payable	0.167
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	123,274	255,740
Common Class A [Member] | Exercise Price Exceeds Market Price [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	128,530	502,269
Common Class B [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		28,765
Common Class B [Member] | Exercise Price Exceeds Market Price [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	49,320	65,071