Note 11 - Stockholders' Equity and Earnings Per Share - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Beginning balance, loss, net of tax	$ 2,294,283	$ 2,121,866	$ 1,973,304
Total other comprehensive (loss)/income, net of tax	3,008	20,308	(6,424)
Ending balance, loss, net of tax	2,418,144	2,294,283	2,121,866
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Beginning balance, loss, net of tax	5,714	(17,765)
Net unrealized (losses)/gains arising during the period, pre-tax	10,903	33,543
Net unrealized (losses)/gains arising during the period, tax	3,223	9,915
Net unrealized (losses)/gains arising during the period, net of tax	7,680	23,628
Reclassification adjustment for net losses/(gains) included in net income, pre-tax	1,695	211
Reclassification adjustment for net losses/(gains) included in net income, tax	501	62
Reclassification adjustment for net losses/(gains) included in net income, net of tax	1,194	149
Total other comprehensive (loss)/income, pre-tax	9,208	33,332
Total other comprehensive (loss)/income, tax	2,722	9,853
Total other comprehensive (loss)/income, net of tax	6,486	23,479
Ending balance, loss, net of tax	12,200	5,714	(17,765)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]
Beginning balance, loss, net of tax	(3,412)	(241)
Net unrealized (losses)/gains arising during the period, pre-tax	(4,938)	(4,502)
Net unrealized (losses)/gains arising during the period, tax	(1,460)	(1,331)
Net unrealized (losses)/gains arising during the period, net of tax	(3,478)	(3,171)
Reclassification adjustment for net losses/(gains) included in net income, pre-tax	0	0
Reclassification adjustment for net losses/(gains) included in net income, tax	0	0
Reclassification adjustment for net losses/(gains) included in net income, net of tax	0	0
Total other comprehensive (loss)/income, pre-tax	(4,938)	(4,502)
Total other comprehensive (loss)/income, tax	(1,460)	(1,331)
Total other comprehensive (loss)/income, net of tax	(3,478)	(3,171)
Ending balance, loss, net of tax	(6,890)	(3,412)	(241)
AOCI Attributable to Parent [Member]
Beginning balance, loss, net of tax	2,302	(18,006)	(2,511)
Net unrealized (losses)/gains arising during the period, pre-tax	5,965	29,041
Net unrealized (losses)/gains arising during the period, tax	1,763	8,584
Net unrealized (losses)/gains arising during the period, net of tax	4,202	20,457
Reclassification adjustment for net losses/(gains) included in net income, pre-tax	1,695	211
Reclassification adjustment for net losses/(gains) included in net income, tax	501	62
Reclassification adjustment for net losses/(gains) included in net income, net of tax	1,194	149
Total other comprehensive (loss)/income, pre-tax	4,270	28,830
Total other comprehensive (loss)/income, tax	1,262	8,522
Total other comprehensive (loss)/income, net of tax	3,008	20,308	(6,424)
Ending balance, loss, net of tax	$ 5,310	$ 2,302	$ (18,006)