Loans and Leases - Age Analysis of Past Due Loans and Leases (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	$ 4,355,389	$ 4,460,111
Accruing loans and leases	5,217,517	5,275,149
Total nonaccrual loans and lease	34,528	31,692
Loans and leases held for investment	5,252,045	5,306,841	$ 5,211,856
Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	6,600	16,173
Financial Asset, 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	1,105	2,218
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	2,204	1,392
Financial Asset Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	9,909	19,783
Financial Asset Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	5,207,608	5,255,366
Commercial Financial And Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	927,015	892,665
Accruing loans and leases	926,082	889,838
Total nonaccrual loans and lease	933	2,827
Loans and leases held for investment	927,015	892,665	894,314
Commercial Financial And Agricultural [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	1,177	1,104
Commercial Financial And Agricultural [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	49	279
Commercial Financial And Agricultural [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	2,000	50
Commercial Financial And Agricultural [Member] | Financial Asset Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	3,226	1,433
Commercial Financial And Agricultural [Member] | Financial Asset Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	922,856	888,405
Paycheck Protection Program Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	85,601	483,773
Accruing loans and leases	85,601	483,773
Total nonaccrual loans and lease	0	0
Loans and leases held for investment	85,601	483,773	501,580
Paycheck Protection Program Loans | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	95	0
Paycheck Protection Program Loans | Financial Asset, 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	0	0
Paycheck Protection Program Loans | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	0	0
Paycheck Protection Program Loans | Financial Asset Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	95	0
Paycheck Protection Program Loans | Financial Asset Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	85,506	483,773
Real-Estate Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	2,669,898	2,458,872
Accruing loans and leases	2,641,602	2,436,133
Total nonaccrual loans and lease	28,296	22,739
Loans and leases held for investment	2,669,898	2,458,872	2,369,691
Real-Estate Commercial [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	1,343	3,230
Real-Estate Commercial [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	0	859
Real-Estate Commercial [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	0	945
Real-Estate Commercial [Member] | Financial Asset Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	1,343	5,034
Real-Estate Commercial [Member] | Financial Asset Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	2,640,259	2,431,099
Real-Estate Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	260,874	243,355
Accruing loans and leases	260,874	243,355
Total nonaccrual loans and lease	0	0
Loans and leases held for investment	260,874	243,355	233,590
Real-Estate Construction [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	0	361
Real-Estate Construction [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	0	0
Real-Estate Construction [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	0	0
Real-Estate Construction [Member] | Financial Asset Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	0	361
Real-Estate Construction [Member] | Financial Asset Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	260,874	242,994
Real Estate Residential Secured For Business Purpose [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	412,001	381,446
Accruing loans and leases	409,532	378,660
Total nonaccrual loans and lease	2,469	2,786
Loans and leases held for investment	412,001	381,446	378,239
Real Estate Residential Secured For Business Purpose [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	789	3,726
Real Estate Residential Secured For Business Purpose [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	344	603
Real Estate Residential Secured For Business Purpose [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	0	0
Real Estate Residential Secured For Business Purpose [Member] | Financial Asset Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	1,133	4,329
Real Estate Residential Secured For Business Purpose [Member] | Financial Asset Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	408,399	374,331
Real Estate-Residential Secured For Personal Purpose [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	535,705	487,600
Accruing loans and leases	533,626	485,514
Total nonaccrual loans and lease	2,079	2,086
Loans and leases held for investment	535,705	487,600	474,688
Real Estate-Residential Secured For Personal Purpose [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	2,025	6,057
Real Estate-Residential Secured For Personal Purpose [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	0	80
Real Estate-Residential Secured For Personal Purpose [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	0	0
Real Estate-Residential Secured For Personal Purpose [Member] | Financial Asset Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	2,025	6,137
Real Estate-Residential Secured For Personal Purpose [Member] | Financial Asset Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	531,601	479,377
Real Estate Home Equity Secured For Personal Purpose [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	159,029	166,609
Accruing loans and leases	158,308	165,562
Total nonaccrual loans and lease	721	1,047
Loans and leases held for investment	159,029	166,609	172,448
Real Estate Home Equity Secured For Personal Purpose [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	301	607
Real Estate Home Equity Secured For Personal Purpose [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	42	32
Real Estate Home Equity Secured For Personal Purpose [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	0	0
Real Estate Home Equity Secured For Personal Purpose [Member] | Financial Asset Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	343	639
Real Estate Home Equity Secured For Personal Purpose [Member] | Financial Asset Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	157,965	164,923
Loans to Individuals [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	26,458	27,482
Accruing loans and leases	26,458	27,482
Total nonaccrual loans and lease	0	0
Loans and leases held for investment	26,458	27,482	27,771
Loans to Individuals [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	215	190
Loans to Individuals [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	16	74
Loans to Individuals [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	58	185
Loans to Individuals [Member] | Financial Asset Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	289	449
Loans to Individuals [Member] | Financial Asset Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	26,169	27,033
Lease Financings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	175,464	165,039
Accruing loans and leases	175,434	164,832
Total nonaccrual loans and lease	30	207
Loans and leases held for investment	175,464	165,039	$ 159,535
Lease Financings [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	655	898
Lease Financings [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	654	291
Lease Financings [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	146	212
Lease Financings [Member] | Financial Asset Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	1,455	1,401
Lease Financings [Member] | Financial Asset Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financial receivables, gross	$ 173,979	$ 163,431