Note 15 - Share-based Compensation - Valuation of Option Grants Under Stock Plans (Details)	3 Months Ended
	Jun. 30, 2020	[1]
Expected volatility	32.90%
Weighted-average volatility	32.90%
Expected dividends	4.48%
Risk-free rate	0.50%
Average risk-free rate	0.50%
Expected term (in years) (Year)	7 years 4 months 24 days
Pre-vesting executive departure rate	0.60%
Pre-vesting non-executive departure rate	2.50%

[1] Stock options were only granted during the second quarter of 2020. There have been no stock options granted since June 30, 2020.