Note 1 - Nature of Business and Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2016

Notes Tables

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	2016			2015			2014
Dividend yield	.35%	to	.51%	.37%	to	.46%		.47%
Expected volatility	29.32%	to	29.37%	28.92%	to	29.32%	29.07%	to	29.18%
Risk-free interest rate	1.73%	to	2.18%	1.89%	to	2.37%	2.69%	to	2.82%
Expected life of option grants (years)		6			6			6
Weighted-average grant date fair value		$7.31			$5.11			$5.68

	2016			2015			2014
Dividend yield	.33%	to	.59%	.37%	to	.45%	.46%	to	.47%
Expected volatility	12.70%	to	15.60%	8.81%	to	13.10%	16.96%	to	19.35%
Risk-free interest rate	.39%	to	.57%	.09%	to	.16%	.04%	to	.12%
Expected life of purchase grants (months)	3	to	6	3	to	6	3	to	6
Weighted-average grant date fair value		$3.28			$2.39			$2.37