Loans and Leases - Allowance for Loan and Lease Losses and Recorded Investment in Loans and Leases (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	$ 585		$ 2,108
Ending balance: pooled	82,459		33,223
Total: Allowance for Credit Loss	83,044	$ 35,331	35,331	$ 29,364	$ 21,555
Loans and Leases Held for Investment [Abstract]
Ending balance: individually analyzed	31,485		38,403
Ending balance: pooled	5,275,169		4,348,116
Loans measured at fair value	187		317
Total loans and leases held for investment	5,306,841		4,386,836
Commercial, Financial and Agricultural [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	535		44
Ending balance: pooled	13,049		8,715
Total: Allowance for Credit Loss	13,584	8,759	8,759	7,983	6,742
Loans and Leases Held for Investment [Abstract]
Ending balance: individually analyzed	2,827		3,442
Ending balance: pooled	889,838		943,587
Loans measured at fair value	0		0
Total loans and leases held for investment	892,665		947,029
Paycheck Protection Program Loans [Member]
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	483,773
Loans measured at fair value	0
Total loans and leases held for investment	483,773		0
Real Estate-Commercial [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	52,230
Total: Allowance for Credit Loss	52,230	15,750	15,750
Loans and Leases Held for Investment [Abstract]
Ending balance: individually analyzed	22,739
Ending balance: pooled	2,435,946
Loans measured at fair value	187
Total loans and leases held for investment	2,458,872		2,040,441
Real Estate-Construction [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	3,298
Total: Allowance for Credit Loss	3,298	2,446	2,446
Loans and Leases Held for Investment [Abstract]
Ending balance: individually analyzed	0
Ending balance: pooled	243,355
Loans measured at fair value	0
Total loans and leases held for investment	243,355		232,595
Real Estate-Commercial and Construction [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed			1,562
Ending balance: pooled			16,634
Total: Allowance for Credit Loss			18,196	13,903	9,839
Loans and Leases Held for Investment [Abstract]
Ending balance: individually analyzed			28,185
Ending balance: pooled			2,244,534
Loans measured at fair value			317
Total loans and leases held for investment			2,273,036
Real Estate-Residential Secured for Business Purpose [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	24		306
Ending balance: pooled	7,293		2,316
Total: Allowance for Credit Loss	7,317	2,622	2,622	2,236	1,661
Loans and Leases Held for Investment [Abstract]
Ending balance: individually analyzed	2,786		2,980
Ending balance: pooled	378,660		370,993
Loans measured at fair value	0		0
Total loans and leases held for investment	381,446		373,973
Real Estate-Residential Secured for Personal Purpose [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	26
Ending balance: pooled	3,029
Total: Allowance for Credit Loss	3,055	2,713	2,713
Loans and Leases Held for Investment [Abstract]
Ending balance: individually analyzed	2,086
Ending balance: pooled	485,514
Loans measured at fair value	0
Total loans and leases held for investment	487,600		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	1,176
Total: Allowance for Credit Loss	1,176	1,076	1,076
Loans and Leases Held for Investment [Abstract]
Ending balance: individually analyzed	1,047
Ending balance: pooled	165,562
Loans measured at fair value	0
Total loans and leases held for investment	166,609		174,435
Real Estate-Residential and Home Equity Secured for Personal Purpose [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed			196
Ending balance: pooled			3,593
Total: Allowance for Credit Loss			3,789	3,199	1,754
Loans and Leases Held for Investment [Abstract]
Ending balance: individually analyzed			3,519
Ending balance: pooled			609,975
Loans measured at fair value			0
Total loans and leases held for investment			613,494
Loans to Individuals [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0		0
Ending balance: pooled	533		470
Total: Allowance for Credit Loss	533	470	470	484	373
Loans and Leases Held for Investment [Abstract]
Ending balance: individually analyzed	0		0
Ending balance: pooled	27,482		29,883
Loans measured at fair value	0		0
Total loans and leases held for investment	27,482		29,883
Lease Financings [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: individually analyzed	0		0
Ending balance: pooled	1,701		1,311
Total: Allowance for Credit Loss	1,701	1,311	1,311	1,288	1,132
Loans and Leases Held for Investment [Abstract]
Ending balance: individually analyzed	0		277
Ending balance: pooled	165,039		149,144
Loans measured at fair value	0		0
Total loans and leases held for investment	165,039		149,421
Unallocated [Member]
Allowance For Credit Losses, Loans And Leases [Abstract]
Ending balance: pooled	150		184
Total: Allowance for Credit Loss	$ 150	$ 184	$ 184	$ 271	$ 54