Allowance for Credit Losses (Portfolio Credit Quality By Loan Class) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($) loan	Dec. 31, 2019 USD ($)
Loan portfolio by credit quality indicator
Portfolio, total	$ 7,501,807	$ 6,894,946
Number of additional relationships reclassified from Pass to Watch List - Substandard | loan	2
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	$ 3,967,980	3,379,837
Commercial, financial and agricultural | Domestic | Commercial
Loan portfolio by credit quality indicator
Portfolio, total	1,807,491	1,292,660
Commercial, financial and agricultural | Domestic | Commercial | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,668,592	1,228,110
Commercial, financial and agricultural | Domestic | Commercial | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	72,066	569
Commercial, financial and agricultural | Domestic | Commercial | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	64,148	39
Commercial, financial and agricultural | Domestic | Commercial | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	1,089	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	1,971,634	1,896,747
Commercial, financial and agricultural | Domestic | Commercial Real Estate: farmland and commercial | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,826,749	1,710,446
Commercial, financial and agricultural | Domestic | Commercial Real Estate: farmland and commercial | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	9,442	13,184
Commercial, financial and agricultural | Domestic | Commercial Real Estate: farmland and commercial | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	69,260	20,183
Commercial, financial and agricultural | Domestic | Commercial Real Estate: farmland and commercial | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	65,647	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	188,855	190,430
Commercial, financial and agricultural | Domestic | Commercial Real Estate: multifamily | Pass
Loan portfolio by credit quality indicator
Portfolio, total	188,718	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	2,277,991	2,185,883
Real estate - construction | Domestic | Commercial Real Estate: other construction and land development
Loan portfolio by credit quality indicator
Portfolio, total	2,277,991	2,185,883
Real estate - construction | Domestic | Commercial Real Estate: other construction and land development | Pass
Loan portfolio by credit quality indicator
Portfolio, total	2,216,065	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	16,106	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	44,530	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	376	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	1,081,380	1,140,377
Real estate - mortgage | Domestic | Residential First Lien
Loan portfolio by credit quality indicator
Portfolio, total	421,538	433,901
Real estate - mortgage | Domestic | Residential First Lien | Pass
Loan portfolio by credit quality indicator
Portfolio, total	420,781	426,546
Real estate - mortgage | Domestic | Residential First Lien | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	245	253
Real estate - mortgage | Domestic | Residential First Lien | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	143	144
Real estate - mortgage | Domestic | Residential First Lien | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	117	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	659,842	706,476
Real estate - mortgage | Domestic | Residential Junior Lien | Pass
Loan portfolio by credit quality indicator
Portfolio, total	658,991	704,958
Real estate - mortgage | Domestic | Residential Junior Lien | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	810	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	42,401	47,800
Consumer | Domestic
Loan portfolio by credit quality indicator
Portfolio, total	42,401	47,800
Consumer | Domestic | Pass
Loan portfolio by credit quality indicator
Portfolio, total	42,398	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	132,055	141,049
Foreign | Foreign
Loan portfolio by credit quality indicator
Portfolio, total	132,055	141,049
Foreign | Foreign | Pass
Loan portfolio by credit quality indicator
Portfolio, total	$ 132,055	140,785
Foreign | Foreign | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		$ 264