Allowance for Loan Losses Composition (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		$ 5,434,000			$ 5,230,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		80,074,000			51,181,000
Acquired with deteriorated credit quality		167,000			268,000
Financing Receivable, Allowance for Credit Losses		85,675,000			56,679,000
Financing Receivable, Individually Evaluated for Impairment		108,407,000			77,459,000
Financing Receivable, Collectively Evaluated for Impairment		7,058,225,000			6,409,614,000
Loans acquired with deteriorated credit quality		11,153,000			14,331,000
Loans and Leases Receivable, Net of Deferred Income		$ 7,177,785,000			$ 6,501,404,000
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Individually Evaluated for Impairment		5.01%			6.75%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Collectively Evaluated for Impairment		1.13%			0.80%
Loans acquired with deteriorated credit quality		1.50%			1.87%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans		1.19%			0.87%
Loans And Leases Receivable, Recorded Investment, Individually Evaluated for Impairment		$ 108,455,000			$ 77,491,000
Loans And Leases Receivable, Recorded Investment, Collectively Evaluated for Impairment		7,078,699,000			6,428,693,000
Loans acquired with deteriorated credit quality		11,284,000			14,441,000
Loans and Leases Receivable, Recorded Investment		7,198,438,000			6,520,625,000
Total loans		$ 7,177,785,000			$ 6,501,404,000	$ 5,692,132,000
Loans and Leases Receivable, Allowance, Environmental Risk Factor	0.825%	0.855%	0.75%	0.675%	0.60%
PPP loans originated	$ 543,100,000	$ 337,100,000
7000 Hotels, Rooming Houses, Camps and Other Lodging Places
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Collectively Evaluated for Impairment		96,909,000
Loans and Leases Receivable, Net of Deferred Income		181,400,000
Additional Reserve Pandemic Risk		1,391,000
722110 Full-Service Restaurants
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Collectively Evaluated for Impairment		33,409,000
Additional Reserve Pandemic Risk		637,000
5331 Retail, Variety Stores
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Collectively Evaluated for Impairment		177,706,000
Additional Reserve Pandemic Risk		1,731,000
Hotels, Restaurants, Strip Shopping Total
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Collectively Evaluated for Impairment		308,024,000
Additional Reserve Pandemic Risk		3,759,000
Purchased credit impaired [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans		10,422,000			$ 13,469,000
Financial Asset Originated | 7000 Hotels, Rooming Houses, Camps and Other Lodging Places
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Collectively Evaluated for Impairment		93,090,000
Additional Reserve Pandemic Risk		1,800,000
Financial Asset Originated | 722110 Full-Service Restaurants
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Collectively Evaluated for Impairment		27,880,000
Financial Asset Originated | 5331 Retail, Variety Stores
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Collectively Evaluated for Impairment		156,605,000
Financial Asset Originated | Hotels, Restaurants, Strip Shopping Total
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Collectively Evaluated for Impairment		277,575,000
Financial Asset Acquired and No Credit Deterioration | 7000 Hotels, Rooming Houses, Camps and Other Lodging Places
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Collectively Evaluated for Impairment		3,819,000
Financial Asset Acquired and No Credit Deterioration | 722110 Full-Service Restaurants
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Collectively Evaluated for Impairment		5,529,000
Financial Asset Acquired and No Credit Deterioration | 5331 Retail, Variety Stores
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Collectively Evaluated for Impairment		21,101,000
Financial Asset Acquired and No Credit Deterioration | Hotels, Restaurants, Strip Shopping Total
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Collectively Evaluated for Impairment		30,449,000
Commercial Financial And Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		3,758,000			5,104,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		21,809,000			14,948,000
Acquired with deteriorated credit quality		41,000			151,000
Financing Receivable, Allowance for Credit Losses		25,608,000			20,203,000
Financing Receivable, Individually Evaluated for Impairment		28,811,000			33,077,000
Financing Receivable, Collectively Evaluated for Impairment		1,559,842,000			1,151,073,000
Loans acquired with deteriorated credit quality		336,000			960,000
Loans and Leases Receivable, Net of Deferred Income		$ 1,588,989,000			$ 1,185,110,000
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Individually Evaluated for Impairment		13.04%			15.43%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Collectively Evaluated for Impairment		1.40%			1.30%
Loans acquired with deteriorated credit quality		12.20%			15.73%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans		1.61%			1.70%
Loans And Leases Receivable, Recorded Investment, Individually Evaluated for Impairment		$ 28,836,000			$ 33,088,000
Loans And Leases Receivable, Recorded Investment, Collectively Evaluated for Impairment		1,566,344,000			1,155,449,000
Loans acquired with deteriorated credit quality		337,000			966,000
Loans and Leases Receivable, Recorded Investment		1,595,517,000			1,189,503,000
Commercial Financial And Agricultural [Member] | Purchased credit impaired [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans		337,000			966,000
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		1,316,000			35,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		22,093,000			10,187,000
Acquired with deteriorated credit quality		71,000			7,000
Financing Receivable, Allowance for Credit Losses		23,480,000			10,229,000
Financing Receivable, Individually Evaluated for Impairment		70,334,000			41,770,000
Financing Receivable, Collectively Evaluated for Impairment		1,670,510,000			1,558,550,000
Loans acquired with deteriorated credit quality		7,345,000			9,093,000
Loans and Leases Receivable, Net of Deferred Income		$ 1,748,189,000			$ 1,609,413,000
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Individually Evaluated for Impairment		1.87%			0.08%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Collectively Evaluated for Impairment		1.32%			0.65%
Loans acquired with deteriorated credit quality		0.97%			0.08%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans		1.34%			0.64%
Loans And Leases Receivable, Recorded Investment, Individually Evaluated for Impairment		$ 70,357,000			$ 41,791,000
Loans And Leases Receivable, Recorded Investment, Collectively Evaluated for Impairment		1,676,388,000			1,564,011,000
Loans acquired with deteriorated credit quality		7,461,000			9,182,000
Loans and Leases Receivable, Recorded Investment		1,754,206,000			1,614,984,000
Commercial Real Estate Portfolio Segment [Member] | Purchased credit impaired [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans		7,461,000			9,182,000
Construction Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		0			0
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		7,288,000			5,311,000
Acquired with deteriorated credit quality		0			0
Financing Receivable, Allowance for Credit Losses		7,288,000			5,311,000
Financing Receivable, Individually Evaluated for Impairment		3,110,000			453,000
Financing Receivable, Collectively Evaluated for Impairment		339,312,000			330,106,000
Loans acquired with deteriorated credit quality		999,000			1,140,000
Loans and Leases Receivable, Net of Deferred Income		$ 343,421,000			$ 331,699,000
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Individually Evaluated for Impairment		0.00%			0.00%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Collectively Evaluated for Impairment		2.15%			1.61%
Loans acquired with deteriorated credit quality		0.00%			0.00%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans		2.12%			1.60%
Loans And Leases Receivable, Recorded Investment, Individually Evaluated for Impairment		$ 3,110,000			$ 453,000
Loans And Leases Receivable, Recorded Investment, Collectively Evaluated for Impairment		340,116,000			331,161,000
Loans acquired with deteriorated credit quality		1,002,000			1,143,000
Loans and Leases Receivable, Recorded Investment		344,228,000			332,757,000
Residential Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		16,000			42,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		11,292,000			8,458,000
Acquired with deteriorated credit quality		55,000			110,000
Financing Receivable, Allowance for Credit Losses		11,363,000			8,610,000
Financing Receivable, Individually Evaluated for Impairment		4,557,000			2,025,000
Financing Receivable, Collectively Evaluated for Impairment		1,806,126,000			1,888,088,000
Loans acquired with deteriorated credit quality		2,361,000			2,613,000
Loans and Leases Receivable, Net of Deferred Income		$ 1,813,044,000			$ 1,892,726,000
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Individually Evaluated for Impairment		0.35%			2.07%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Collectively Evaluated for Impairment		0.63%			0.45%
Loans acquired with deteriorated credit quality		2.33%			4.21%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans		0.63%			0.45%
Loans And Leases Receivable, Recorded Investment, Individually Evaluated for Impairment		$ 4,557,000			$ 2,025,000
Loans And Leases Receivable, Recorded Investment, Collectively Evaluated for Impairment		1,808,892,000			1,891,941,000
Loans acquired with deteriorated credit quality		2,372,000			2,625,000
Loans and Leases Receivable, Recorded Investment		1,815,821,000			1,896,591,000
Consumer Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		0			0
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		17,418,000			12,211,000
Acquired with deteriorated credit quality		0			0
Financing Receivable, Allowance for Credit Losses		17,418,000			12,211,000
Financing Receivable, Individually Evaluated for Impairment		0			0
Financing Receivable, Collectively Evaluated for Impairment		1,659,704,000			1,452,373,000
Loans acquired with deteriorated credit quality		0			2,000
Loans and Leases Receivable, Net of Deferred Income		$ 1,659,704,000			$ 1,452,375,000
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Individually Evaluated for Impairment		0.00%			0.00%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Collectively Evaluated for Impairment		1.05%			0.84%
Loans acquired with deteriorated credit quality		0.00%			0.00%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans		1.05%			0.84%
Loans And Leases Receivable, Recorded Investment, Individually Evaluated for Impairment		$ 0			$ 0
Loans And Leases Receivable, Recorded Investment, Collectively Evaluated for Impairment		1,664,214,000			1,456,687,000
Loans acquired with deteriorated credit quality		0			2,000
Loans and Leases Receivable, Recorded Investment		1,664,214,000			1,456,689,000
Leases
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		344,000			49,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment		174,000			66,000
Acquired with deteriorated credit quality		0			0
Financing Receivable, Allowance for Credit Losses		518,000			115,000
Financing Receivable, Individually Evaluated for Impairment		1,595,000			134,000
Financing Receivable, Collectively Evaluated for Impairment		22,731,000			29,424,000
Loans acquired with deteriorated credit quality		112,000			523,000
Loans and Leases Receivable, Net of Deferred Income		$ 24,438,000			$ 30,081,000
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Individually Evaluated for Impairment		21.57%			36.57%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans, Collectively Evaluated for Impairment		0.77%			0.22%
Loans acquired with deteriorated credit quality		0.00%			0.00%
Loans And Leases Receivable, Ratio Of Allowance For Loan Losses To Total Loans		2.12%			0.38%
Loans And Leases Receivable, Recorded Investment, Individually Evaluated for Impairment		$ 1,595,000			$ 134,000
Loans And Leases Receivable, Recorded Investment, Collectively Evaluated for Impairment		22,745,000			29,444,000
Loans acquired with deteriorated credit quality		112,000			523,000
Loans and Leases Receivable, Recorded Investment		24,452,000			30,101,000
Leases | Purchased credit impaired [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans		112,000			523,000
Commercial Portfolio Segment [Member] | Performing acquired loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		678,000
Commercial Portfolio Segment [Member] | Financial Asset Acquired with Credit Deterioration [Member] | Purchased credit impaired [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment		$ 167,000			268,000
Commercial Portfolio Segment [Member] | Financial Asset Acquired with Credit Deterioration [Member] | Nonperforming Financial Instruments [Member] | Purchased credit impaired [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment					0
Loans and Leases Receivable, Recorded Investment					6,000
Total loans					$ 5,000