Note 15 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

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

	Year Ended December 31,
	2019			2018			2017
Risk–free interest rate		2.30	%		2.46	%		2.08	%
Expected volatility		17.4	%		16.1	%		16.6	%
Expected life, in years		2.3			3.0			4.8
Expected dividend yield		2.73	%		3.29	%		3.10	%

Share-based Payment Arrangement, Option, Activity [Table Text Block]

	Number of Shares			Weighted Average Exercise Price		Aggregate Intrinsic Value
Options outstanding at January 1, 2017		177,959			55.48		−
Options granted		1,125,443			72.96		−
Options exercised		(48,995	)		51.25		−
Options cancelled		(15,000	)		72.94		−
Options outstanding at December 31, 2017		1,239,407			71.19		–
Options granted		110,265			61.39		–
Options exercised		(68,291	)		54.31		–
Options cancelled		(118,000	)		72.11		–
Options outstanding at December 31, 2018		1,163,381			71.16		–
Options granted		53,316			77.89		–
Options exercised		(346,168	)		71.57		–
Options cancelled		(85,000	)		72.94		–
Options outstanding at December 31, 2019		785,529		$	71.24	$	11,931,000
Options exercisable at December 31, 2019		204,029		$	68.20	$	3,720,000

Share-based Payment Arrangement, Option, Exercise Price Range [Table Text Block]

Options Outstanding December 31, 2019		Exercise Prices				Weighted Average Exercise Price		Weighted Average Remaining Contractual Life in Years
	139,968		$60.73	–	62.78	$	61.81		2.1
	645,561		$72.94	–	$77.92		73.29		2.3
	785,529					$	71.24		2.3