Loans and Leases - Allowance for Loan and Lease Losses and Recorded Investment in Loans and Leases (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	$ 356			$ 1,135
Ending balance: pooled	70,999			85,082
Financing Receivable, Allowance for Credit Loss	71,355	$ 71,497	$ 83,044	86,217	$ 68,216	$ 35,331
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	33,498			25,775
Ending balance: pooled	5,293,697			4,925,779
Loans measured at fair value	118			255
Total loans and leases held for investment	5,327,313		5,306,841	4,951,809
Commercial Financial And Agricultural [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	333			905
Ending balance: pooled	11,401			15,831
Financing Receivable, Allowance for Credit Loss	11,734	10,233	13,584	16,736	19,244	8,759
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	1,246			4,208
Ending balance: pooled	919,375			818,525
Loans measured at fair value	0			0
Total loans and leases held for investment	920,621		892,665	822,733
Paycheck Protection Program Loans
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	3			0
Financing Receivable, Allowance for Credit Loss	3	0	0	0
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	252,849			498,978
Loans measured at fair value	0			0
Total loans and leases held for investment	252,849		483,773	498,978
Real-Estate Commercial [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			19
Ending balance: pooled	43,194			50,652
Financing Receivable, Allowance for Credit Loss	43,194	45,459	52,230	50,671	34,810	15,750
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	26,264			17,568
Ending balance: pooled	2,574,537			2,204,667
Loans measured at fair value	118			255
Total loans and leases held for investment	2,600,919		2,458,872	2,222,490
Real-Estate Construction [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	3,649			4,130
Financing Receivable, Allowance for Credit Loss	3,649	2,799	3,298	4,130	3,117
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	274,529			212,534
Loans measured at fair value	0			0
Total loans and leases held for investment	274,529		243,355	212,534
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	6,747			8,179
Financing Receivable, Allowance for Credit Loss	6,747	6,692	7,317	8,180	5,906	2,622
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	3,045			1,754
Ending balance: pooled	404,619			374,296
Loans measured at fair value	0			0
Total loans and leases held for investment	407,664		381,446	376,050
Real Estate Residential Secured For Personal Purpose [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	23			210
Ending balance: pooled	2,597			2,459
Financing Receivable, Allowance for Credit Loss	2,620	3,056	3,055	2,669	2,121
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	2,160			1,268
Ending balance: pooled	511,170			461,244
Loans measured at fair value	0			0
Total loans and leases held for investment	513,330		487,600	462,512
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	1,124			1,071
Financing Receivable, Allowance for Credit Loss	1,124	1,257	1,176	1,071	795
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	783			977
Ending balance: pooled	159,235			172,064
Loans measured at fair value	0			0
Total loans and leases held for investment	160,018		166,609	173,041
Loans to Individuals [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	319			771
Financing Receivable, Allowance for Credit Loss	319	447	533	771	600	470
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	25,845			29,222
Loans measured at fair value	0			0
Total loans and leases held for investment	25,845		27,482	29,222
Lease Financings [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	1,815			1,839
Financing Receivable, Allowance for Credit Loss	1,815	1,404	1,701	1,839	1,473	1,311
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	171,538			154,249
Loans measured at fair value	0			0
Total loans and leases held for investment	171,538		165,039	154,249
Unallocated [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: pooled	150			150
Financing Receivable, Allowance for Credit Loss	$ 150	$ 150	$ 150	$ 150	$ 150	$ 184