Note 1 - Summary of Significant Accounting Policies - Cumulative Effect of Changes (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for credit losses on loans	$ 136,157		$ 166,538
Deferred tax assets			85,610
Allowance for unfunded commitments			5,880
Stockholders' equity	$ 2,446,251		$ 2,418,144	$ 2,294,283	$ 2,121,866
Cumulative Effect, Period of Adoption, Adjustment [Member]
Allowance for credit losses on loans		$ (1,560)
Deferred tax assets		1,319
Allowance for unfunded commitments		6,018
Stockholders' equity		(3,139)
Cumulative Effect, Period of Adoption, Adjusted Balance [Member]
Allowance for credit losses on loans		164,978
Deferred tax assets		86,929
Allowance for unfunded commitments		11,898
Stockholders' equity		$ 2,415,005