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Allowance for Credit Losses (Portfolio Credit Quality By Loan Class) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Loan portfolio by credit quality indicator
Portfolio, total	$ 7,589,235	$ 6,894,946
Pass
Loan portfolio by credit quality indicator
Portfolio, total		6,538,085
Special Review
Loan portfolio by credit quality indicator
Portfolio, total		33,553
Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total		62,315
Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total		248,318
Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		12,675
Commercial, financial and agricultural
Loan portfolio by credit quality indicator
Portfolio, total	4,426,866	3,379,837
Commercial, financial and agricultural | Domestic | Commercial
Loan portfolio by credit quality indicator
Portfolio, total	1,877,979	1,292,660
Commercial, financial and agricultural | Domestic | Commercial | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,736,598	1,228,110
Commercial, financial and agricultural | Domestic | Commercial | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	73,297	569
Commercial, financial and agricultural | Domestic | Commercial | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	65,664	39
Commercial, financial and agricultural | Domestic | Commercial | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	976	62,007
Commercial, financial and agricultural | Domestic | Commercial | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		1,935
Commercial, financial and agricultural | Domestic | Commercial Real Estate: farmland and commercial
Loan portfolio by credit quality indicator
Portfolio, total	2,110,950	1,896,747
Commercial, financial and agricultural | Domestic | Commercial Real Estate: farmland and commercial | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,964,241	1,710,446
Commercial, financial and agricultural | Domestic | Commercial Real Estate: farmland and commercial | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	9,567	13,184
Commercial, financial and agricultural | Domestic | Commercial Real Estate: farmland and commercial | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	71,162	20,183
Commercial, financial and agricultural | Domestic | Commercial Real Estate: farmland and commercial | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	65,479	151,726
Commercial, financial and agricultural | Domestic | Commercial Real Estate: farmland and commercial | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		1,208
Commercial, financial and agricultural | Domestic | Commercial Real Estate: multifamily
Loan portfolio by credit quality indicator
Portfolio, total	437,937	190,430
Commercial, financial and agricultural | Domestic | Commercial Real Estate: multifamily | Pass
Loan portfolio by credit quality indicator
Portfolio, total	437,800	190,265
Commercial, financial and agricultural | Domestic | Commercial Real Estate: multifamily | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		165
Real estate - construction
Loan portfolio by credit quality indicator
Portfolio, total	1,943,430	2,185,883
Real estate - construction | Domestic | Commercial Real Estate: other construction and land development
Loan portfolio by credit quality indicator
Portfolio, total	1,943,430	2,185,883
Real estate - construction | Domestic | Commercial Real Estate: other construction and land development | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,883,596	2,090,370
Real estate - construction | Domestic | Commercial Real Estate: other construction and land development | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	12,625	18,721
Real estate - construction | Domestic | Commercial Real Estate: other construction and land development | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	27,529	41,949
Real estate - construction | Domestic | Commercial Real Estate: other construction and land development | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	18,769	33,905
Real estate - construction | Domestic | Commercial Real Estate: other construction and land development | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		938
Real estate - mortgage
Loan portfolio by credit quality indicator
Portfolio, total	1,033,646	1,140,377
Real estate - mortgage | Domestic | Residential First Lien
Loan portfolio by credit quality indicator
Portfolio, total	410,015	433,901
Real estate - mortgage | Domestic | Residential First Lien | Pass
Loan portfolio by credit quality indicator
Portfolio, total	409,514	426,546
Real estate - mortgage | Domestic | Residential First Lien | Special Review
Loan portfolio by credit quality indicator
Portfolio, total		253
Real estate - mortgage | Domestic | Residential First Lien | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	146	144
Real estate - mortgage | Domestic | Residential First Lien | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	112	680
Real estate - mortgage | Domestic | Residential First Lien | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		6,278
Real estate - mortgage | Domestic | Residential Junior Lien
Loan portfolio by credit quality indicator
Portfolio, total	623,631	706,476
Real estate - mortgage | Domestic | Residential Junior Lien | Pass
Loan portfolio by credit quality indicator
Portfolio, total	621,952	704,958
Real estate - mortgage | Domestic | Residential Junior Lien | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	1,641	826
Real estate - mortgage | Domestic | Residential Junior Lien | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		692
Consumer
Loan portfolio by credit quality indicator
Portfolio, total	41,110	47,800
Consumer | Domestic
Loan portfolio by credit quality indicator
Portfolio, total	41,110	47,800
Consumer | Domestic | Pass
Loan portfolio by credit quality indicator
Portfolio, total	41,107	46,605
Consumer | Domestic | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		1,195
Foreign
Loan portfolio by credit quality indicator
Portfolio, total	144,183	141,049
Foreign | Foreign
Loan portfolio by credit quality indicator
Portfolio, total	144,183	141,049
Foreign | Foreign | Pass
Loan portfolio by credit quality indicator
Portfolio, total	$ 144,183	140,785
Foreign | Foreign | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		$ 264

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Reference 1: http://www.xbrl.org/2003/role/exampleRef
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