Note 11 - Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2016

Notes Tables

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

	2016			2015
Risk–free interest rate		0.61	%		0.71	%
Expected volatility		14.9	%		16.5	%
Expected life, in years (years)	1.0			2.2
Expected dividend yield		2.74	%		2.73	%

Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]

	Number of Shares			Weighted Average Exercise Price		Aggregate Intrinsic Value
Options outstanding at January 1, 2015		954,678		$	46.92	$	–
Options granted		56,210			61.47		–
Options exercised		(389,498	)		47.06		–
Options outstanding at December 31, 2015		621,390			48.15		–
Options granted		12,239			61.59		–
Options exercised		(465,275	)		47.06		–
Options forfeited		(656	)		46.69
Options outstanding at March 31, 2016		167,698		$	53.01	$	1,557,000
Options exercisable at March 31, 2016		155,459		$	52.34	$	1,548,000

Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block]

Options Outstanding March 31, 2016	Exercise Prices				Weighted Average Exercise Price		Weighted Average Remaining Contractual Life in Years
112,500		$44.80	-	52.93	$	48.94		2.2
55,198		$61.25	-	61.59		61.33		3.3
167,698					$	53.01		2.6