Loans and Leases - Reserve for Loan and Lease Losses and Recorded Investment in Loans and Leases (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	$ 1,135			$ 2,439
Ending balance: pooled	85,082			30,161
Total ending balance	86,217	$ 68,216	$ 35,331	32,600	$ 31,602	$ 29,364
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	25,775			25,102
Ending balance: pooled	4,925,779			4,141,077
Loans measured at fair value	255			1,725
Total loans and leases held for investment	4,951,809		4,386,836	4,167,904
Commercial Financial And Agricultural [Member]
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	905			99
Ending balance: pooled	15,831			9,030
Total ending balance	16,736	19,244	8,759	9,129	8,950	7,983
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	4,208			2,150
Ending balance: pooled	818,525			934,999
Loans measured at fair value	0			0
Total loans and leases held for investment	822,733		947,029	937,149
Paycheck Protection Program Loans
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	0
Total ending balance	0
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	498,978
Loans measured at fair value	0
Total loans and leases held for investment	498,978		0
Real-Estate Commercial [Member]
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	19
Ending balance: pooled	50,652
Total ending balance	50,671	34,810	15,750
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	17,568
Ending balance: pooled	2,204,667
Loans measured at fair value	255
Total loans and leases held for investment	2,222,490		2,040,441
Real-Estate Construction [Member]
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	4,130
Total ending balance	4,130	3,117	2,446
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	212,534
Loans measured at fair value	0
Total loans and leases held for investment	212,534		232,595
Real Estate Commercial And Construction [Member]
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed				1,840
Ending balance: pooled				13,638
Total ending balance				15,478	14,981	13,903
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed				17,845
Ending balance: pooled				2,073,036
Loans measured at fair value				1,725
Total loans and leases held for investment				2,092,606
Real Estate Residential Secured For Business Purpose [Member]
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	1			165
Ending balance: pooled	8,179			2,313
Total ending balance	8,180	5,906	2,622	2,478	2,302	2,236
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	1,754			1,596
Ending balance: pooled	374,296			364,044
Loans measured at fair value	0			0
Total loans and leases held for investment	376,050		373,973	365,640
Real Estate Residential Secured For Personal Purpose [Member]
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	210
Ending balance: pooled	2,459
Total ending balance	2,669	2,121	2,713
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	1,268
Ending balance: pooled	461,244
Loans measured at fair value	0
Total loans and leases held for investment	462,512		439,059
Real Estate Home Equity Secured For Personal Purpose [Member]
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	1,071
Total ending balance	1,071	795	1,076
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	977
Ending balance: pooled	172,064
Loans measured at fair value	0
Total loans and leases held for investment	173,041		174,435
Residential And Home Equity Secured For Personal Purpose [Member]
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed				335
Ending balance: pooled				3,183
Total ending balance				3,518	3,379	3,199
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed				3,511
Ending balance: pooled				594,226
Loans measured at fair value				0
Total loans and leases held for investment				597,737
Loans to Individuals [Member]
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	771			481
Total ending balance	771	600	470	481	469	484
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	29,222			32,485
Loans measured at fair value	0			0
Total loans and leases held for investment	29,222		29,883	32,485
Lease Financings [Member]
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	1,839			1,241
Total ending balance	1,839	1,473	1,311	1,241	1,275	1,288
Loans and leases held for investment [Abstract]
Ending balance: individually analyzed	0			0
Ending balance: pooled	154,249			142,287
Loans measured at fair value	0			0
Total loans and leases held for investment	154,249		149,421	142,287
Unallocated [Member]
Reserve For Credit Losses, Loans And Leases [Abstract]
Ending balance: pooled	150			275
Total ending balance	$ 150	$ 150	$ 184	$ 275	$ 246	$ 271