Note 8 - Earnings Per Share - Net Income Per Share Computation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Net income	$ 7,715	$ 11,755	$ 7,393	$ 8,196	$ 19,470	$ 15,589
Allocation of distributed and undistributed income to unvested restricted stock shareholders	(15)		(25)		(38)	(53)
Net income attributable to common shareholders	$ 7,700		$ 7,368		$ 19,432	$ 15,536
Weighted average common shares outstanding – basic (in shares)	25,148		24,789		25,060	24,777
Net income per share – basic (in dollars per share)	$ 0.31		$ 0.30		$ 0.78	$ 0.63
Net income attributable to common shareholders for basic computation	$ 7,700		$ 7,368		$ 19,432	$ 15,536
Weighted average effect of dilutive securities – stock options (in shares)	532		797		642	772
Denominator for diluted earnings per share – adjusted weighted average shares (in shares)	25,680		25,586		25,702	25,549
Net income per share - diluted (in dollars per share)	$ 0.30		$ 0.29		$ 0.76	$ 0.61