Note 10 - Net Income per Share - Computation of Basic and Diluted Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic:
Net income	$ 5,184	$ 4,624	$ 3,513	$ 4,314	$ 8,751	$ 3,853	$ 13,321	$ 16,918
Weighted average shares outstanding (in shares)	19,871			19,503			19,731	19,369
Basic earnings per share (in dollars per share)	$ 0.26			$ 0.22			$ 0.68	$ 0.87
Diluted:
Net income	$ 5,184	$ 4,624	$ 3,513	$ 4,314	$ 8,751	$ 3,853	$ 13,321	$ 16,918
Weighted average shares outstanding (in shares)	19,871			19,503			19,731	19,369
Common stock equivalents, if dilutive (in shares)	507			790			546	889
Shares used in computing diluted earnings per common share (in shares)	20,378			20,293			20,277	20,258
Diluted earnings per share (in dollars per share)	$ 0.25			$ 0.21			$ 0.66	$ 0.84
Shares excluded in computing diluted earnings per share as those shares would be anti-dilutive (in shares)	210			212			488	213