Note 9 - Share-based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Notes Tables

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

	2020			2019			2018
	Common Stock			Common Stock			Common Stock
Expected dividend yield at date of grant		1.84	%		2.60	%		2.59	%
Expected stock price volatility		33.62	%		34.01	%		32.47	%
Risk-free interest rate		1.35	%		2.38	%		2.51	%
Expected life of options (in years)		7.39			7.46			7.28

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

	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Terms (Years)		Aggregate Intrinsic Value (In thousands)
Common Stock
Outstanding at December 31, 2019		1,245,922		$	18.08
Granted		70,471		$	62.23
Exercised		(630,373	)	$	14.20			$	25,912
Forfeited		(85,449	)	$	32.28
Outstanding at December 31, 2020		600,571		$	25.31		5.58	$	11,665
Exercisable at December 31, 2020		270,876		$	18.00		4.14	$	6,811

Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value, Intrinsic Value of Exercised and Vested in Period, and Fair Value of Vested in Period [Table Text Block]

	2020		2019		2018
	Common Stock		Common Stock		Common Stock
Weighted average grant date fair value of stock options granted	$	18.67	$	11.99	$	10.02
Intrinsic value of stock options exercised (in thousands)	$	25,912	$	8,280	$	10,621
Intrinsic value of stock options vested (in thousands)	$	1,965	$	1,891	$	2,719

Schedule of Nonvested Share Activity [Table Text Block]

	Common Stock Outstanding			Common Stock Weighted Average Grant Date Fair Value Per Share
Outstanding at December 31, 2019		84,176		$	17.23
Granted		--		$	--
Vested		(71,378	)	$	13.59
Forfeited		(6,793	)	$	36.80
Outstanding at December 31, 2020		6,005		$	38.30