Note 1 - Nature of Business and Significant Accounting Policies (Details) - Option Pricing Model Valuation Assumptions - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Note 1 - Nature of Business and Significant Accounting Policies (Details) - Option Pricing Model Valuation Assumptions [Line Items]
Expected life of option grants	10 years
Weighted-average grant date fair value (in Dollars per share)	$ 5.11	$ 5.68	$ 5.14
Employee Stock Option [Member]
Note 1 - Nature of Business and Significant Accounting Policies (Details) - Option Pricing Model Valuation Assumptions [Line Items]
Dividend yield		0.47%
Expected volatility
Risk-free interest rate
Expected life of option grants	6 years	6 years	6 years
Weighted-average grant date fair value (in Dollars per share)	$ 5.11	$ 5.68	$ 5.14
Stock Purchase Grants [Member]
Note 1 - Nature of Business and Significant Accounting Policies (Details) - Option Pricing Model Valuation Assumptions [Line Items]
Dividend yield
Expected volatility
Risk-free interest rate
Expected life of option grants
Weighted-average grant date fair value (in Dollars per share)	$ 2.39	$ 2.37	$ 2.10
Minimum [Member] | Employee Stock Option [Member]
Note 1 - Nature of Business and Significant Accounting Policies (Details) - Option Pricing Model Valuation Assumptions [Line Items]
Dividend yield	0.37%		0.44%
Expected volatility	28.92%	29.07%	29.50%
Risk-free interest rate	1.89%	2.69%	1.71%
Minimum [Member] | Stock Purchase Grants [Member]
Note 1 - Nature of Business and Significant Accounting Policies (Details) - Option Pricing Model Valuation Assumptions [Line Items]
Dividend yield	0.37%	0.46%	0.53%
Expected volatility	8.81%	16.96%	23.05%
Risk-free interest rate	0.09%	0.04%	0.10%
Expected life of option grants	3 years	3 years	3 years
Maximum [Member] | Employee Stock Option [Member]
Note 1 - Nature of Business and Significant Accounting Policies (Details) - Option Pricing Model Valuation Assumptions [Line Items]
Dividend yield	0.46%		0.53%
Expected volatility	29.32%	29.18%	30.56%
Risk-free interest rate	2.37%	2.82%	2.90%
Maximum [Member] | Stock Purchase Grants [Member]
Note 1 - Nature of Business and Significant Accounting Policies (Details) - Option Pricing Model Valuation Assumptions [Line Items]
Dividend yield	0.45%	0.47%	0.61%
Expected volatility	13.10%	19.35%	24.25%
Risk-free interest rate	0.16%	0.12%	0.18%
Expected life of option grants	6 years	6 years	6 years