Note 5 - Stock Options Valuation Assumptions (Details)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Common Class A [Member]
Expected dividend yield at date of grant	3.02%	2.57%
Expected stock price volatility	34.61%	34.87%
Risk-free interest rate	2.12%	1.78%
Expected life of options (in years)	8 years	7 years
Common Class B [Member]
Expected dividend yield at date of grant	8.12%	5.72%
Expected stock price volatility	31.77%	33.94%
Risk-free interest rate	2.12%	1.78%
Expected life of options (in years)	8 years	7 years