Note 11 - Common Stock and Stock-based Compensation Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands		9 Months Ended		12 Months Ended
		Sep. 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 9 months 18 days	[2]	3 years 7 months 6 days
Outstanding, Aggregated intrinsic value		$ 2,978	[2]	$ 6,673
Exercised, Number of shares (in shares)	[1]	(158,069)
Exercised, Weighted average exercise price (in dollars per share)		$ 24.47
Outstanding, Number of shares (in shares)	[1]	131,000	[2]	289,069
Outstanding, Weighted average exercise price (in dollars per share)		$ 19.94	[2]	$ 22.42
Exercisable, Number of shares (in shares)	[1],[3]	131,000
Exercisable, Weighted average exercise price (in dollars per share)	[3]	$ 19.94
Exercisable, Weighted average remaining contractual term (Year)	[3]	2 years 9 months 18 days
Exercisable, Aggregated intrinsic value	[3]	$ 2,978

[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 128,000 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 128,000 shares of the Company’s common stock issuable upon exercise.