Note 7 - Share-based Compensation - Stock-settled Stock Appreciation Rights Transactions (Details) - Stock Appreciation Rights (SARs) [Member] - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2021	Dec. 31, 2020
Outstanding SARS (in shares)		317,128
Outstanding SARS, weighted average exercise price (in dollars per share)		$ 13.47
Outstanding SARS, weighted average remaining life (Year)		3 years 4 months 9 days	3 years 4 months 9 days
Outstanding SARS, aggregate intrinsic value		$ 3,744	$ 2,031
Granted SARs (in shares)	[1]	31,687
Granted SARS, weighted average exercise price (in dollars per share)	[1]	$ 25.75
Exercised SARs (in shares)		(7,018)
Exercised SARS, weighted average exercise price (in dollars per share)		$ 18.86
Outstanding SARS (in shares)		341,797	317,128
Outstanding SARS, weighted average exercise price (in dollars per share)		$ 14.50	$ 13.47
Exercisable (in shares)		108,203
Exercisable, weighted average exercise price (in dollars per share)		$ 19.64
Exercisable, weighted average remaining life (Year)		1 year 10 months 6 days
Exercisable, aggregate intrinsic value		$ 625

[1] The weighted average grant date fair value of SARs granted was $10.09 per share.