Note 3 - Earnings Per Share - Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net income		$ 17,333	$ 10,179	$ 42,668	$ 35,164
Divided by:
Weighted average common shares outstanding (in shares)		28,604	29,120	28,806	29,092
Weighted average common stock equivalents (in shares)			1	1	2
Total weighted average common shares outstanding and common stock equivalents (in shares)		28,604	29,121	28,807	29,094
Basic earnings per common share (in dollars per share)		$ 0.61	$ 0.35	$ 1.48	$ 1.21
Diluted earnings per common share (in dollars per share)	[1]	$ 0.61	$ 0.35	$ 1.48	$ 1.21
Dividend payout ratio		32.80%	51.40%	40.50%	44.60%

[1] For the three and nine months ended September 30, 2018 and 2017, there were no common stock equivalents that were anti-dilutive.