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Allowance for Probable Loan Losses (Aging By Loan Class) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing receivable recorded investment
Past due 90 days or Greater and Still Accruing	$ 7,052	$ 40,674
Past due	36,122	75,833
Loans, current	6,806,579	6,485,456
Total loans	6,842,701	6,561,289
30 to 59 Days
Financing receivable recorded investment
Past due	10,876	15,978
60 to 89 Days
Financing receivable recorded investment
Past due	8,237	6,011
90 Days or Greater
Financing receivable recorded investment
Past due	17,009	53,844
Commercial
Financing receivable recorded investment
Past due 90 days or Greater and Still Accruing	1,312	10,890
Past due	12,696	25,591
Loans, current	1,190,047	1,103,378
Total loans	1,202,743	1,128,969
Commercial | 30 to 59 Days
Financing receivable recorded investment
Past due	3,160	4,651
Commercial | 60 to 89 Days
Financing receivable recorded investment
Past due	696	1,089
Commercial | 90 Days or Greater
Financing receivable recorded investment
Past due	8,840	19,851
Commercial Real Estate:Other Construction and Land Development
Financing receivable recorded investment
Past due 90 days or Greater and Still Accruing	206	16
Past due	1,338	3,356
Loans, current	2,008,860	1,882,875
Total loans	2,010,198	1,886,231
Commercial Real Estate:Other Construction and Land Development | 30 to 59 Days
Financing receivable recorded investment
Past due	308	727
Commercial Real Estate:Other Construction and Land Development | 60 to 89 Days
Financing receivable recorded investment
Past due		1,707
Commercial Real Estate:Other Construction and Land Development | 90 Days or Greater
Financing receivable recorded investment
Past due	1,030	922
Commercial Real Estate: Farmland and Commercial
Financing receivable recorded investment
Past due 90 days or Greater and Still Accruing	325	24,910
Past due	7,145	30,951
Loans, current	2,020,851	1,918,947
Total loans	2,027,996	1,949,898
Commercial Real Estate: Farmland and Commercial | 30 to 59 Days
Financing receivable recorded investment
Past due	1,534	2,928
Commercial Real Estate: Farmland and Commercial | 60 to 89 Days
Financing receivable recorded investment
Past due	4,844	784
Commercial Real Estate: Farmland and Commercial | 90 Days or Greater
Financing receivable recorded investment
Past due	767	27,239
Commercial Real Estate: Multifamily
Financing receivable recorded investment
Past due 90 days or Greater and Still Accruing		71
Past due	660	1,505
Loans, current	220,771	224,752
Total loans	221,431	226,257
Commercial Real Estate: Multifamily | 30 to 59 Days
Financing receivable recorded investment
Past due		927
Commercial Real Estate: Multifamily | 60 to 89 Days
Financing receivable recorded investment
Past due	155
Commercial Real Estate: Multifamily | 90 Days or Greater
Financing receivable recorded investment
Past due	505	578
Residential First Lien
Financing receivable recorded investment
Past due 90 days or Greater and Still Accruing	3,948	3,079
Past due	8,363	9,037
Loans, current	451,815	436,763
Total loans	460,178	445,800
Residential First Lien | 30 to 59 Days
Financing receivable recorded investment
Past due	2,632	3,998
Residential First Lien | 60 to 89 Days
Financing receivable recorded investment
Past due	1,419	1,677
Residential First Lien | 90 Days or Greater
Financing receivable recorded investment
Past due	4,312	3,362
Residential Junior Lien
Financing receivable recorded investment
Past due 90 days or Greater and Still Accruing	1,070	937
Past due	2,367	2,881
Loans, current	722,897	724,420
Total loans	725,264	727,301
Residential Junior Lien | 30 to 59 Days
Financing receivable recorded investment
Past due	633	1,155
Residential Junior Lien | 60 to 89 Days
Financing receivable recorded investment
Past due	374	618
Residential Junior Lien | 90 Days or Greater
Financing receivable recorded investment
Past due	1,360	1,108
Consumer
Financing receivable recorded investment
Past due 90 days or Greater and Still Accruing	24	32
Past due	881	550
Loans, current	45,832	45,766
Total loans	46,713	46,316
Consumer | 30 to 59 Days
Financing receivable recorded investment
Past due	742	486
Consumer | 60 to 89 Days
Financing receivable recorded investment
Past due	111	19
Consumer | 90 Days or Greater
Financing receivable recorded investment
Past due	28	45
Foreign
Financing receivable recorded investment
Past due 90 days or Greater and Still Accruing	167	739
Past due	2,672	1,962
Loans, current	145,506	148,555
Total loans	148,178	150,517
Foreign | 30 to 59 Days
Financing receivable recorded investment
Past due	1,867	1,106
Foreign | 60 to 89 Days
Financing receivable recorded investment
Past due	638	117
Foreign | 90 Days or Greater
Financing receivable recorded investment
Past due	$ 167	$ 739

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