Note 7 - Share-based Compensation - Stock Option Transactions (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2021	Dec. 31, 2020
Outstanding, options (in shares)		970,022
Outstanding, weighted average exercise price (in dollars per share)		$ 12.92
Outstanding, weighted average remaining life (Year)		3 years 8 months 19 days	3 years 8 months 26 days
Outstanding, aggregate intrinsic value		$ 11,821	$ 11,128
Granted (in shares)	[1]	100,513
Granted, weighted average exercise price (in dollars per share)	[1]	$ 25.75
Exercised (in shares)		(18,907)
Exercised, weighted average exercise price (in dollars per share)		$ 17.42
Lapsed or cancelled (in shares)		(12,740)
Lapsed or cancelled, weighted average exercise price (in dollars per share)		$ 14.09
Outstanding, options (in shares)		1,038,888	970,022
Outstanding, weighted average exercise price (in dollars per share)		$ 14.07	$ 12.92
Exercisable, options (in shares)		355,111
Exercisable, weighted average exercise price, options (in dollars per share)		$ 17.49
Exercisable, weighted average remaining life, options (Year)		2 years 5 months 12 days
Exercisable, aggregate intrinsic value, options		$ 2,816

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