Note 9 - Stockholders' Equity - Options Classified Into Range of Exercise Price (Details) - $ / shares		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018
Outstanding, number of options and SARs (in shares)	[2]	642,253	[1]	702,817
Outstanding, Weighted average remaining contractual term (Year)		3 years 182 days	[1]	4 years 109 days
Outstanding, weighted average exercise price (in dollars per share)		$ 20.14
Exercisable, Number of shares (in shares)	[2],[3]	616,253
Exercisable, weighted average remaining contractual life (Year)		3 years 146 days
Exercisable, Weighted average exercise price (in dollars per share)	[3]	$ 19.80
Exercise Price Range 1 [Member]
Range of exercise price, lower limit (in dollars per share)		14.16
Range of exercise price, upper limit (in dollars per share)		$ 18.62
Outstanding, number of options and SARs (in shares)		299,836
Outstanding, Weighted average remaining contractual term (Year)		2 years 182 days
Outstanding, weighted average exercise price (in dollars per share)		$ 15.64
Exercisable, Number of shares (in shares)		299,836
Exercisable, weighted average remaining contractual life (Year)		2 years 182 days
Exercisable, Weighted average exercise price (in dollars per share)		$ 15.64
Exercise Price Range 2 [Member]
Range of exercise price, lower limit (in dollars per share)		19.36
Range of exercise price, upper limit (in dollars per share)		$ 19.83
Outstanding, number of options and SARs (in shares)		172,166
Outstanding, Weighted average remaining contractual term (Year)		4 years 36 days
Outstanding, weighted average exercise price (in dollars per share)		$ 19.42
Exercisable, Number of shares (in shares)		172,166
Exercisable, weighted average remaining contractual life (Year)		4 years 36 days
Exercisable, Weighted average exercise price (in dollars per share)		$ 19.42
Exercise Price Range 3 [Member]
Range of exercise price, lower limit (in dollars per share)		24.86
Range of exercise price, upper limit (in dollars per share)		$ 30.60
Outstanding, number of options and SARs (in shares)		170,251
Outstanding, Weighted average remaining contractual term (Year)		4 years 292 days
Outstanding, weighted average exercise price (in dollars per share)		$ 28.81
Exercisable, Number of shares (in shares)		144,251
Exercisable, weighted average remaining contractual life (Year)		4 years 146 days
Exercisable, Weighted average exercise price (in dollars per share)		$ 28.88

[1] Due to the ceiling imposed on the SAR grants, the outstanding amount equals a maximum of 596,877 shares of the Company's common stock issuable upon exercise.

[2] 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.

[3] Due to the ceiling imposed on the SAR grants, the exercisable amount equals a maximum of 570,877 shares of the Company's common stock issuable upon exercise.