Note 3 - Earnings Per Common Share - Summary of Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Weighted average common shares outstanding (in shares)	53,893,753	53,544,747	53,817,928	53,508,710
Net income available to common stockholders	$ 43,362	$ 37,563	$ 118,557	$ 108,175
Basic earnings per common share (in dollars per share)	$ 0.80	$ 0.70	$ 2.20	$ 2.02
Dilutive effects of assumed conversions and exercise of stock options and warrants (in shares)	339,212	551,621	380,494	578,700
Weighted average common and dilutive potential common shares outstanding (in shares)	54,232,965	54,096,368	54,198,422	54,087,410
Net income available to common stockholders	$ 43,362	$ 37,563	$ 118,557	$ 108,175
Diluted earnings per common share (in dollars per share)	$ 0.80	$ 0.69	$ 2.19	$ 2.00