Note 2 - Income Per Share - Calculation of Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net income	$ 6,071	$ 4,433	$ 9,971	$ 4,417	$ 10,504	$ 14,388
Denominator:
Denominator for basic income per share – weighted-average shares (in shares)	18,438		18,337		18,410	18,334
Effect of dilutive securities:
Equivalent shares issuable upon conversion of unvested restricted shares (in shares)	168		104		160	90
Diluted weighted average shares outstanding (in shares)	18,606		18,441		18,570	18,424
Income per share:
Basic and diluted income per share (in dollars per share)	$ 0.33		$ 0.54		$ 0.57	$ 0.78