Allowance for Credit Losses (Impaired Loans) (Details)	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Aug. 05, 2020 USD ($)
Recorded investment:
Total impaired loans with related allowance				$ 636,000
Total impaired loans with no related allowance				12,039,000
Unpaid principal balance:
Total impaired loans with an allowance recorded				685,000
Total impaired loans with no related allowance recorded				13,255,000
Related Allowance				365,000
Average recorded investment:
Total impaired loans with an allowance recorded	$ 3,817,000		$ 3,824,000	645,000
Total impaired loans with no related allowance recorded	42,125,000		48,909,000	65,192,000
Interest Recognized
Total impaired loans with no related allowance recorded	93,000		182,000	368,000
Total trouble debt restructuring		$ 5,760,000		7,788,000
Amount of loans with some degree of payment deferred		1,853,640,000
Loans		$ 7,501,807,000		6,894,946,000
Period of charge off for past due unsecured commercial loans		90 days
Paycheck protection program loans
Interest Recognized
Period of time PPP loans cover payroll and certain other costs		168 days
Interest rate on receivable		1.00%
Number of loans approved and closed					4,914
Amount of loans approved and closed					$ 454,259,000
Paycheck protection program loans | Loans made prior to June 5, 2020
Interest Recognized
Term of receivable (in years)		2 years
Paycheck protection program loans | Loans made after June 5, 2020
Interest Recognized
Term of receivable (in years)		5 years
Commercial, financial and agricultural
Interest Recognized
Loans		$ 3,967,980,000		3,379,837,000
Commercial, financial and agricultural | Domestic | Commercial
Recorded investment:
Total impaired loans with related allowance				510,000
Total impaired loans with no related allowance				1,425,000
Unpaid principal balance:
Total impaired loans with an allowance recorded				516,000
Total impaired loans with no related allowance recorded				1,516,000
Related Allowance				249,000
Average recorded investment:
Total impaired loans with an allowance recorded	1,316,000		1,322,000	514,000
Total impaired loans with no related allowance recorded	16,788,000		17,078,000	16,194,000
Interest Recognized
Total impaired loans with no related allowance recorded	1,000		1,000	3,000
Total trouble debt restructuring				32,000
Loans		1,807,491,000		1,292,660,000
Commercial, financial and agricultural | Domestic | Commercial Real Estate: farmland and commercial
Recorded investment:
Total impaired loans with no related allowance				1,208,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded				1,841,000
Average recorded investment:
Total impaired loans with an allowance recorded	2,369,000		2,369,000
Total impaired loans with no related allowance recorded	14,203,000		20,551,000	36,632,000
Interest Recognized
Loans		1,971,634,000		1,896,747,000
Commercial, financial and agricultural | Domestic | Commercial Real Estate: multifamily
Recorded investment:
Total impaired loans with no related allowance				165,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded				168,000
Average recorded investment:
Total impaired loans with no related allowance recorded	507,000		507,000	565,000
Interest Recognized
Loans		188,855,000		190,430,000
Real estate - construction
Interest Recognized
Loans		2,277,991,000		2,185,883,000
Real estate - construction | Domestic | Commercial Real Estate: other construction and land development
Recorded investment:
Total impaired loans with related allowance				126,000
Total impaired loans with no related allowance				812,000
Unpaid principal balance:
Total impaired loans with an allowance recorded				169,000
Total impaired loans with no related allowance recorded				1,133,000
Related Allowance				116,000
Average recorded investment:
Total impaired loans with an allowance recorded	132,000		133,000	131,000
Total impaired loans with no related allowance recorded	1,792,000		1,813,000	2,151,000
Interest Recognized
Loans		2,277,991,000		2,185,883,000
Real estate - mortgage
Interest Recognized
Loans		1,081,380,000		1,140,377,000
Real estate - mortgage | Domestic | Residential First Lien
Recorded investment:
Total impaired loans with no related allowance				6,278,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded				6,445,000
Average recorded investment:
Total impaired loans with no related allowance recorded	6,480,000		6,579,000	7,136,000
Interest Recognized
Total impaired loans with no related allowance recorded	78,000		153,000	305,000
Total trouble debt restructuring		3,834,000		5,608,000
Loans		421,538,000		433,901,000
Real estate - mortgage | Domestic | Residential Junior Lien
Recorded investment:
Total impaired loans with no related allowance				692,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded				692,000
Average recorded investment:
Total impaired loans with no related allowance recorded	1,028,000		1,033,000	976,000
Interest Recognized
Total impaired loans with no related allowance recorded	11,000		22,000	44,000
Total trouble debt restructuring		670,000		692,000
Loans		659,842,000		706,476,000
Consumer
Interest Recognized
Loans		42,401,000		47,800,000
Consumer | Domestic
Recorded investment:
Total impaired loans with no related allowance				1,195,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded				1,196,000
Average recorded investment:
Total impaired loans with no related allowance recorded	1,046,000		1,063,000	1,211,000
Interest Recognized
Total impaired loans with no related allowance recorded				2,000
Total trouble debt restructuring		1,007,000		1,192,000
Loans		42,401,000		47,800,000
Foreign
Interest Recognized
Loans		132,055,000		141,049,000
Foreign | Foreign
Recorded investment:
Total impaired loans with no related allowance				264,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded				264,000
Average recorded investment:
Total impaired loans with no related allowance recorded	281,000		285,000	327,000
Interest Recognized
Total impaired loans with no related allowance recorded	$ 3,000		$ 6,000	14,000
Total trouble debt restructuring		249,000		264,000
Loans		$ 132,055,000		$ 141,049,000