Note 7 - Earnings Per Share (Details Textual)	3 Months Ended		6 Months Ended
	Jun. 30, 2017 shares	Jun. 30, 2016 shares	Jun. 30, 2017 shares	Jun. 30, 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	104,835	66,428	115,908	260,868
Common Class A [Member] | Exercise Price Exceeds Market Price [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		798,421	52,707	550,561
Common Class B [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		34,830	19,318	34,333
Common Class B [Member] | Exercise Price Exceeds Market Price [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	17,473	46,813	38,784	38,407