Note 22 - Regulatory Matters - Capital and Leverage Ratios (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Common equity Tier 1 capital ( to risk-weighted assets)		$ 1,736,854	$ 1,572,025
Common equity Tier 1 capital ( to risk-weighted assets)		12.43%	12.19%
Common equity Tier 1 capital minimum requirement		$ 628,393	$ 580,552
Common equity Tier 1 capital minimum requirement		4.50%	4.50%
Excess Common equtiy Tier 1 capital		$ 1,108,461	$ 991,473
Excess Common equtiy Tier 1 capital		7.93%	7.69%
Tier 1 capital (to risk-weighted assets)		$ 1,736,854	$ 1,572,025
Tier 1 capital (to risk-weighted assets)		12.43%	12.19%
Tier 1 capital minimum requirement		$ 838,258	$ 774,070
Tier 1 capital minimum requirement		6.00%	6.00%
Excess Tier 1 capital		$ 898,596	$ 797,955
Excess Tier 1 capital		6.43%	6.19%
Total capital (to risk-weighted assets)		$ 1,976,995	$ 1,820,860
Total capital (to risk-weighted assets)		14.15%	14.11%
Total capital minimum requirement		$ 1,117,677	$ 1,032,093
Total capital minimum requirement		8.00%	8.00%
Excess Total capital		$ 859,318	$ 788,767
Excess Total capital		6.15%	6.11%
Tier 1 capital (to average assets) – Leverage ratio		$ 1,736,854	$ 1,572,025
Tier 1 capital (to average assets) – Leverage ratio		10.83%	10.35%
Minimum leverage requirement		$ 641,755	$ 607,349
Minimum leverage requirement		4.00%	4.00%
Excess Tier One Leverage Capital		$ 1,095,099	$ 964,676
Excess Tier One Leverage Capital		6.83%	6.35%
Risk-weighted assets		$ 13,969,004	$ 12,901,161
Total average assets (1)	[1]	16,042,924	15,183,720
Bank [Member]
Common equity Tier 1 capital ( to risk-weighted assets)		$ 1,904,820	$ 1,734,719
Common equity Tier 1 capital ( to risk-weighted assets)		13.66%	13.46%
Common equity Tier 1 capital minimum requirement		$ 627,800	$ 579,921
Common equity Tier 1 capital minimum requirement		4.50%	4.50%
Excess Common equtiy Tier 1 capital		$ 1,277,020	$ 1,154,798
Excess Common equtiy Tier 1 capital		9.16%	8.96%
Tier 1 capital (to risk-weighted assets)		$ 1,904,820	$ 1,734,719
Tier 1 capital (to risk-weighted assets)		13.66%	13.46%
Tier 1 capital minimum requirement		$ 837,067	$ 773,229
Tier 1 capital minimum requirement		6.00%	6.00%
Excess Tier 1 capital		$ 1,067,753	$ 961,490
Excess Tier 1 capital		7.66%	7.46%
Total capital (to risk-weighted assets)		$ 2,029,462	$ 1,862,806
Total capital (to risk-weighted assets)		14.55%	14.45%
Total capital minimum requirement		$ 1,116,089	$ 1,030,971
Total capital minimum requirement		8.00%	8.00%
Excess Total capital		$ 913,373	$ 831,835
Excess Total capital		6.55%	6.45%
Tier 1 capital (to average assets) – Leverage ratio		$ 1,904,820	$ 1,734,719
Tier 1 capital (to average assets) – Leverage ratio		11.89%	11.82%
Minimum leverage requirement		$ 640,807	$ 586,959
Minimum leverage requirement		4.00%	4.00%
Excess Tier One Leverage Capital		$ 1,264,013	$ 1,147,760
Excess Tier One Leverage Capital		7.89%	7.82%
Risk-weighted assets		$ 13,949,605	$ 12,887,142
Total average assets (1)	[1]	$ 16,019,658	$ 14,673,981

[1] The quarterly total average assets reflect all debt securities at amortized cost, equity security with readily determinable fair values at the lower of cost or fair value, and equity securities without readily determinable fair values at historical cost.