Note 15 - Stock-based Compensation - Fair Value of Stock-based Award Using Exercise Multiple-based Lattice SAR Pricing Model Assumptions (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Risk-free interest rate	1.80%	2.80%	1.90%
Expected life (in years) (Year)	3 years 6 months	3 years 6 months	3 years 1 month 6 days
Dividend yield	0.70%	0.90%	0.62%
Expected volatility	25.10%	25.50%	27.20%
Forfeiture rate for directors	8.60%	3.10%
Director [Member] | The 2018 Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member]
Risk-free interest rate	1.79%
Expected life (in years) (Year)	3 years 6 months
Dividend yield	0.57%
Expected volatility	24.80%
Forfeiture rate for directors	0.00%
Sub-Optimal Exercise Factor for directors	2.8