Allowance for Credit Losses (Portfolio Credit Quality By Loan Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Loan portfolio by credit quality indicator
Portfolio, total	$ 7,024,380	$ 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
Loan portfolio by credit quality indicator
Portfolio, total	1,369,011	1,292,660
Commercial | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,230,029	1,228,110
Commercial | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	71,700	569
Commercial | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	37	39
Commercial | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	65,596	62,007
Commercial | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		1,935
Real estate - construction
Loan portfolio by credit quality indicator
Portfolio, total	2,216,740	2,185,883
Real estate - construction | Pass
Loan portfolio by credit quality indicator
Portfolio, total	2,123,482	2,090,370
Real estate - construction | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	16,106	18,721
Real estate - construction | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	43,992	41,949
Real estate - construction | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	32,224	33,905
Real estate - construction | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		938
Commercial Real Estate: Farmland and Commercial
Loan portfolio by credit quality indicator
Portfolio, total	1,933,365	1,896,747
Commercial Real Estate: Farmland and Commercial | Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,751,855	1,710,446
Commercial Real Estate: Farmland and Commercial | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	9,388	13,184
Commercial Real Estate: Farmland and Commercial | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	26,029	20,183
Commercial Real Estate: Farmland and Commercial | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	145,576	151,726
Commercial Real Estate: Farmland and Commercial | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		1,208
Commercial Real Estate: Multifamily
Loan portfolio by credit quality indicator
Portfolio, total	202,450	190,430
Commercial Real Estate: Multifamily | Pass
Loan portfolio by credit quality indicator
Portfolio, total	202,298	190,265
Commercial Real Estate: Multifamily | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		165
Residential First Lien
Loan portfolio by credit quality indicator
Portfolio, total	431,588	433,901
Residential First Lien | Pass
Loan portfolio by credit quality indicator
Portfolio, total	429,896	426,546
Residential First Lien | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	249	253
Residential First Lien | Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	144	144
Residential First Lien | Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	675	680
Residential First Lien | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		6,278
Residential Junior Lien
Loan portfolio by credit quality indicator
Portfolio, total	686,604	706,476
Residential Junior Lien | Pass
Loan portfolio by credit quality indicator
Portfolio, total	685,795	704,958
Residential Junior Lien | Special Review
Loan portfolio by credit quality indicator
Portfolio, total	809	826
Residential Junior Lien | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		692
Consumer
Loan portfolio by credit quality indicator
Portfolio, total	45,440	47,800
Consumer | Pass
Loan portfolio by credit quality indicator
Portfolio, total	45,437	46,605
Consumer | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		1,195
Foreign
Loan portfolio by credit quality indicator
Portfolio, total	139,182	141,049
Foreign | Pass
Loan portfolio by credit quality indicator
Portfolio, total	$ 139,182	140,785
Foreign | Watch - List Impaired
Loan portfolio by credit quality indicator
Portfolio, total		$ 264