Note 12 - Net Income Per Share and Common Stock Dividends - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net income	$ 15,641	$ 13,404
Weighted average shares outstanding - basic (in shares)	22,661	22,577
Dilutive securities (in shares)	285	354
Weighted average shares outstanding- diluted (in shares)	22,946	22,931
Net income per share, basic (in dollars per share)	$ 0.69	$ 0.59
Net income per share, diluted (in dollars per share)	$ 0.68	$ 0.58