Note 10 - Temporal Details of Time-based Vesting Conditions (Details) - Board Of Directors And Management [Member] - Stock Options With Time Based Vesting Conditions [Member] - $ / shares	1 Months Ended
	Jul. 31, 2017	May 31, 2017	Sep. 30, 2016	May 31, 2016	Jan. 31, 2016
Number of Shares	76,500	40,000	20,000	40,000	5,000
ExercisePrice	$ 12.22	$ 19.945	$ 28.48	$ 31.33	$ 27.77
Grant Date Fair Value (in dollars per share)	$ 2.31	$ 3.40		$ 7.57	$ 6.56
Risk-Free Interest Rate		1.81%		1.74%	2.00%
Estimated Volatility		32.00%		40.00%	40.00%
Dividend Yield		5.26%	4.92%	4.47%	5.04%
Expected Life		5 years		5 years	5 years
Maximum [Member]
Grant Date Fair Value (in dollars per share)			$ 4.83
Risk-Free Interest Rate	1.94%		1.50%
Estimated Volatility	33.70%		31.00%
Dividend Yield	5.12%
Expected Life	5 years		7 years
Minimum [Member]
Grant Date Fair Value (in dollars per share)			$ 4.28
Risk-Free Interest Rate	2.08%		1.21%
Estimated Volatility	33.90%		29.00%
Dividend Yield	5.15%
Expected Life	6 years		5 years