Note 22 - Regulatory Matters - Capital and Leverage Ratios (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Common Equity Tier 1 to Risk-Weighted Assets, Actual amount	$ 1,959,832	$ 1,904,820
Common Equity Tier 1 to Risk-Weighted Assets, Actual ratio	12.97%	13.66%
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required	$ 1,057,880	$ 889,287
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required, Ratio	7.00%	6.375%
Common Equity Tier 1 to Risk-Weighted Assets, Required to be Considered Well Capitalized	$ 982,318	$ 906,724
Common Equity Tier 1 to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	6.50%	6.50%
Tier 1 Capital to Risk-Weighted Assets, Actual amount	$ 1,959,832	$ 1,904,820
Tier 1 Capital to Risk-Weighted Assets, Actual ratio	12.97%	13.66%
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required	$ 1,284,569	$ 1,098,531
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required, Ratio	8.50%	7.875%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized	$ 1,209,006	$ 1,115,968
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	8.00%	8.00%
Total Capital to Risk-Weighted Assets, Actual amount	$ 2,086,911	$ 2,029,462
Total Capital to Risk-Weighted Assets, Actual ratio	13.81%	14.55%
Total Capital to Risk-Weighted Assets, Minimum Capital Required	$ 1,586,821	$ 1,377,523
Total Capital to Risk-Weighted Assets, Minimum Capital Required, Ratio	10.50%	9.875%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized	$ 1,511,258	$ 1,394,961
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	10.00%	10.00%
Leverage Ratio, Actual amount	$ 1,959,832	$ 1,904,820
Leverage Ratio, Actual ratio	11.23%	11.89%
Leverage Ratio, Minimum Capital Required	$ 697,976	$ 640,807
Leverage Ratio Minimum Capital Required, Ratio	4.00%	4.00%
Leverage Ratio, Required to be Considered Well Capitalized	$ 872,470	$ 800,983
Leverage Ratio Required to be Considered Well Capitalized, Ratio	5.00%	5.00%
Bank [Member]
Common Equity Tier 1 to Risk-Weighted Assets, Actual amount	$ 1,892,321	$ 1,736,854
Common Equity Tier 1 to Risk-Weighted Assets, Actual ratio	12.51%	12.43%
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required	$ 1,059,259	$ 890,524
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required, Ratio	7.00%	6.375%
Common Equity Tier 1 to Risk-Weighted Assets, Required to be Considered Well Capitalized	$ 983,597	$ 907,985
Common Equity Tier 1 to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	6.50%	6.50%
Tier 1 Capital to Risk-Weighted Assets, Actual amount	$ 1,892,321	$ 1,736,854
Tier 1 Capital to Risk-Weighted Assets, Actual ratio	12.51%	12.43%
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required	$ 1,286,243	$ 1,100,059
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required, Ratio	8.50%	7.875%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized	$ 1,210,581	$ 1,117,520
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	8.00%	8.00%
Total Capital to Risk-Weighted Assets, Actual amount	$ 2,134,900	$ 1,976,995
Total Capital to Risk-Weighted Assets, Actual ratio	14.11%	14.15%
Total Capital to Risk-Weighted Assets, Minimum Capital Required	$ 1,588,888	$ 1,379,439
Total Capital to Risk-Weighted Assets, Minimum Capital Required, Ratio	10.50%	9.875%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized	$ 1,513,227	$ 1,396,900
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	10.00%	10.00%
Leverage Ratio, Actual amount	$ 1,892,321	$ 1,736,854
Leverage Ratio, Actual ratio	10.83%	10.83%
Leverage Ratio, Minimum Capital Required	$ 699,173	$ 641,755
Leverage Ratio Minimum Capital Required, Ratio	4.00%	4.00%
Leverage Ratio, Required to be Considered Well Capitalized	$ 873,966	$ 802,146
Leverage Ratio Required to be Considered Well Capitalized, Ratio	5.00%	5.00%