Loans and Leases - Allowance for Loan and Lease Losses and Recorded Investment in Loans and Leases (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	$ 1,092				$ 2,444
Ending balance: pooled	90,778				31,218
Total: Allowance for Credit Loss	91,870	$ 86,217	$ 35,331	$ 35,331	33,662	$ 32,600	$ 29,364
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	29,767				37,228
Ending balance: pooled	5,181,868				4,214,356
Loans measured at fair value	221				349
Total loans and leases held for investment	5,211,856			4,386,836	4,251,933
Commercial Financial And Agricultural [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	891				390
Ending balance: pooled	13,656				8,860
Total: Allowance for Credit Loss	14,547	16,736	8,759	8,759	9,250	9,129	7,983
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	3,809				2,233
Ending balance: pooled	890,505				956,920
Loans measured at fair value	0				0
Total loans and leases held for investment	894,314			947,029	959,153
Paycheck Protection Program Loans
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	0
Total: Allowance for Credit Loss	0
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	501,580
Loans measured at fair value	0
Total loans and leases held for investment	501,580			0
Real-Estate Commercial [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	19
Ending balance: pooled	58,133
Total: Allowance for Credit Loss	58,152	50,671	15,750	15,750
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	20,464
Ending balance: pooled	2,349,006
Loans measured at fair value	221
Total loans and leases held for investment	2,369,691			2,040,441
Real-Estate Construction [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	4,485
Total: Allowance for Credit Loss	4,485	4,130	2,446	2,446
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	233,590
Loans measured at fair value	0
Total loans and leases held for investment	233,590			232,595
Real Estate Commercial And Construction [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed					1,485
Ending balance: pooled					14,336
Total: Allowance for Credit Loss					15,821	15,478	13,903
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed					28,280
Ending balance: pooled					2,122,066
Loans measured at fair value					349
Total loans and leases held for investment					2,150,695
Real Estate Residential Secured For Business Purpose [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	1				414
Ending balance: pooled	8,365				2,271
Total: Allowance for Credit Loss	8,366	8,180	2,622	2,622	2,685	2,478	2,236
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	2,151				2,887
Ending balance: pooled	376,088				357,834
Loans measured at fair value	0				0
Total loans and leases held for investment	378,239			373,973	360,721
Real Estate Residential Secured For Personal Purpose [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	181
Ending balance: pooled	2,535
Total: Allowance for Credit Loss	2,716	2,669	2,713	2,713
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	2,395
Ending balance: pooled	472,293
Loans measured at fair value	0
Total loans and leases held for investment	474,688			439,059
Real Estate Home Equity Secured For Personal Purpose [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	1,279
Total: Allowance for Credit Loss	1,279	1,071	1,076	1,076
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	948
Ending balance: pooled	171,500
Loans measured at fair value	0
Total loans and leases held for investment	172,448			174,435
Residential And Home Equity Secured For Personal Purpose [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed					155
Ending balance: pooled					3,457
Total: Allowance for Credit Loss					3,612	3,518	3,199
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed					3,520
Ending balance: pooled					606,322
Loans measured at fair value					0
Total loans and leases held for investment					609,842
Loans to Individuals [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0				0
Ending balance: pooled	549				475
Total: Allowance for Credit Loss	549	771	470	470	475	481	484
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0				2
Ending balance: pooled	27,771				30,713
Loans measured at fair value	0				0
Total loans and leases held for investment	27,771			29,883	30,715
Lease Financings [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0				0
Ending balance: pooled	1,626				1,234
Total: Allowance for Credit Loss	1,626	1,839	1,311	1,311	1,234	1,241	1,288
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0				306
Ending balance: pooled	159,535				140,501
Loans measured at fair value	0				0
Total loans and leases held for investment	159,535			149,421	140,807
Unallocated [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: pooled	150				585
Total: Allowance for Credit Loss	$ 150	$ 150	$ 184	$ 184	$ 585	$ 275	$ 271