Loans and Leases - Allowance for Loan and Lease Losses and Recorded Investment in Loans and Leases (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	$ 15			$ 1,092
Ending balance: pooled	70,131			90,778
Financing Receivable, Allowance for Credit Loss	70,146	$ 71,355	$ 83,044	91,870	$ 86,217	$ 35,331
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	34,498			29,767
Ending balance: pooled	5,217,465			5,181,868
Loans measured at fair value	82			221
Total loans and leases held for investment	5,252,045		5,306,841	5,211,856
Commercial Financial And Agricultural [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			891
Ending balance: pooled	12,186			13,656
Financing Receivable, Allowance for Credit Loss	12,186	11,734	13,584	14,547	16,736	8,759
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	933			3,809
Ending balance: pooled	926,082			890,505
Loans measured at fair value	0			0
Total loans and leases held for investment	927,015		892,665	894,314
Paycheck Protection Program Loans
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	2			0
Financing Receivable, Allowance for Credit Loss	2	3	0	0
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	85,601			501,580
Loans measured at fair value	0			0
Total loans and leases held for investment	85,601		483,773	501,580
Real-Estate Commercial [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	15			19
Ending balance: pooled	41,491			58,133
Financing Receivable, Allowance for Credit Loss	41,506	43,194	52,230	58,152	50,671	15,750
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	28,296			20,464
Ending balance: pooled	2,641,520			2,349,006
Loans measured at fair value	82			221
Total loans and leases held for investment	2,669,898		2,458,872	2,369,691
Real-Estate Construction [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	3,854			4,485
Financing Receivable, Allowance for Credit Loss	3,854	3,649	3,298	4,485	4,130	2,446
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	260,874			233,590
Loans measured at fair value	0			0
Total loans and leases held for investment	260,874		243,355	233,590
Real Estate Residential Secured For Business Purpose [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			1
Ending balance: pooled	6,531			8,365
Financing Receivable, Allowance for Credit Loss	6,531	6,747	7,317	8,366	8,180	2,622
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	2,469			2,151
Ending balance: pooled	409,532			376,088
Loans measured at fair value	0			0
Total loans and leases held for investment	412,001		381,446	378,239
Real Estate Residential Secured For Personal Purpose [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			181
Ending balance: pooled	2,491			2,535
Financing Receivable, Allowance for Credit Loss	2,491	2,620	3,055	2,716	2,669	2,713
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	2,079			2,395
Ending balance: pooled	533,626			472,293
Loans measured at fair value	0			0
Total loans and leases held for investment	535,705		487,600	474,688
Real Estate Home Equity Secured For Personal Purpose [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	1,076			1,279
Financing Receivable, Allowance for Credit Loss	1,076	1,124	1,176	1,279	1,071
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	721			948
Ending balance: pooled	158,308			171,500
Loans measured at fair value	0			0
Total loans and leases held for investment	159,029		166,609	172,448
Loans to Individuals [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	354			549
Financing Receivable, Allowance for Credit Loss	354	319	533	549	771	470
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	26,458			27,771
Loans measured at fair value	0			0
Total loans and leases held for investment	26,458		27,482	27,771
Lease Financings [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	2,009			1,626
Financing Receivable, Allowance for Credit Loss	2,009	1,815	1,701	1,626	1,839	1,311
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	175,464			159,535
Loans measured at fair value	0			0
Total loans and leases held for investment	175,464		165,039	159,535
Unallocated [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: pooled	137			150
Financing Receivable, Allowance for Credit Loss	$ 137	$ 150	$ 150	$ 150	$ 150	$ 184