Note 11 - Common Stock and Stock-based Compensation Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands		6 Months Ended		12 Months Ended
		Jun. 30, 2021		Dec. 31, 2020
Outstanding, Number of shares (in shares)	[1]	289,069
Outstanding, Weighted average exercise price (in dollars per share)		$ 22.42
Outstanding, Weighted average remaining contractual term (Year)		2 years 10 months 24 days	[2]	3 years 7 months 6 days
Outstanding, Aggregated intrinsic value		$ 3,742	[2]	$ 6,673
Granted, Number of shares (in shares)	[1]	0
Exercised, Number of shares (in shares)	[1]	(153,295)
Exercised, Weighted average exercise price (in dollars per share)		$ 24.79
Forfeited or expired, Number of shares (in shares)	[1]	0
Forfeited or expired, Weighted average exercise price (in dollars per share)		$ 0
Outstanding, Number of shares (in shares)	[1]	135,774	[2]	289,069
Outstanding, Weighted average exercise price (in dollars per share)		$ 19.74	[2]	$ 22.42
Exercisable, Number of shares (in shares)	[1],[3]	135,774
Exercisable, Weighted average exercise price (in dollars per share)	[3]	$ 19.74
Exercisable, Weighted average remaining contractual term (Year)	[3]	2 years 10 months 24 days
Exercisable, Aggregated intrinsic value	[3]	$ 3,742

[1] The SAR units are convertible for a maximum number of shares of the Company's common stock equal to 75% of the SAR units subject to the grant.

[2] Due to the ceiling imposed on the SAR grants, the outstanding amount equals a maximum of 131,581 shares of the Company’s common stock issuable upon exercise.

[3] Due to the ceiling imposed on the SAR grants, the exercisable amount equals a maximum of 131,581 shares of the Company’s common stock issuable upon exercise.