Note 5 - Share-based Compensation - Stock Options Valuation Assumptions (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Common Class A [Member]
Expected dividend yield at date of grant	2.57%	1.47%
Expected stock price volatility	34.87%	32.03%
Risk-free interest rate	1.78%	2.37%
Expected life of options (in years)	7 years	7 years
Common Class B [Member]
Expected dividend yield at date of grant	5.72%	4.87%
Expected stock price volatility	33.94%	32.65%
Risk-free interest rate	1.78%	2.37%
Expected life of options (in years)	7 years	7 years