Note 3 - Earnings Per Common Share - Summary of Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Weighted average common shares outstanding (in shares)	53,082,322	52,745,335
Net income available to common stockholders	$ 32,603	$ 22,519
Basic earnings per common share (in dollars per share)	$ 0.61	$ 0.43
Dilutive effects of assumed conversions and exercise of stock options and warrants (in shares)	1,101,078	1,388,387
Weighted average common and dilutive potential common shares outstanding (in shares)	54,183,400	54,133,722
Net income available to common stockholders	$ 32,603	$ 22,519
Diluted earnings per common share (in dollars per share)	$ 0.60	$ 0.42