Loans and Leases - Credit Quality Indicators (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	$ 3,629,198	$ 3,081,287
Total Loans and Leases Held for Investment, Acquired	377,376	538,780
Grade: 1. Cash secured/ 2. Fully secured [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	30,566	22,941
Total Loans and Leases Held for Investment, Acquired	0	1,120
Grade: 3. Strong [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	15,460	11,027
Total Loans and Leases Held for Investment, Acquired	0	0
Grade: 4. Satisfactory [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	41,923	57,507
Total Loans and Leases Held for Investment, Acquired	0	607
Grade: 5. Acceptable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	2,075,827	1,846,112
Total Loans and Leases Held for Investment, Acquired	218,256	306,841
Grade: 6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	687,957	491,740
Total Loans and Leases Held for Investment, Acquired	86,672	125,613
Grade: 7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	55,799	18,689
Total Loans and Leases Held for Investment, Acquired	0	18,035
Grade: 8. Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	31,119	42,809
Total Loans and Leases Held for Investment, Acquired	13,619	13,114
Grade: 9. Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Grade: 10. Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Internally Assigned Grades [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	2,938,651	2,490,825
Total Loans and Leases Held for Investment, Acquired	318,547	465,330
Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	689,112	587,990
Total Loans and Leases Held for Investment, Acquired	56,867	72,705
Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	1,435	2,472
Total Loans and Leases Held for Investment, Acquired	1,962	745
Performing and Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	690,547	590,462
Total Loans and Leases Held for Investment, Acquired	58,829	73,450
Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	913,166	833,100
Total Loans and Leases Held for Investment, Acquired	24,519	63,111
Commercial, Financial and Agricultural [Member] | Grade: 1. Cash secured/ 2. Fully secured [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	2,783	2,521
Total Loans and Leases Held for Investment, Acquired	0	1,120
Commercial, Financial and Agricultural [Member] | Grade: 3. Strong [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	14,762	9,206
Total Loans and Leases Held for Investment, Acquired	0	0
Commercial, Financial and Agricultural [Member] | Grade: 4. Satisfactory [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	20,133	30,283
Total Loans and Leases Held for Investment, Acquired	0	125
Commercial, Financial and Agricultural [Member] | Grade: 5. Acceptable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	627,585	593,205
Total Loans and Leases Held for Investment, Acquired	21,468	49,949
Commercial, Financial and Agricultural [Member] | Grade: 6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	217,473	179,990
Total Loans and Leases Held for Investment, Acquired	2,982	6,183
Commercial, Financial and Agricultural [Member] | Grade: 7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	23,287	4,027
Total Loans and Leases Held for Investment, Acquired	0	1,007
Commercial, Financial and Agricultural [Member] | Grade: 8. Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	7,143	13,868
Total Loans and Leases Held for Investment, Acquired	69	4,727
Commercial, Financial and Agricultural [Member] | Grade: 9. Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Commercial, Financial and Agricultural [Member] | Grade: 10. Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Commercial, Financial and Agricultural [Member] | Internally Assigned Grades [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	913,166	833,100
Total Loans and Leases Held for Investment, Acquired	24,519	63,111
Real Estate-Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	1,507,579	1,235,681
Total Loans and Leases Held for Investment, Acquired	233,625	306,460
Real Estate-Commercial [Member] | Grade: 1. Cash secured/ 2. Fully secured [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Commercial [Member] | Grade: 3. Strong [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	698	1,821
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Commercial [Member] | Grade: 4. Satisfactory [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	21,790	26,950
Total Loans and Leases Held for Investment, Acquired	0	482
Real Estate-Commercial [Member] | Grade: 5. Acceptable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	1,118,288	960,258
Total Loans and Leases Held for Investment, Acquired	145,722	183,490
Real Estate-Commercial [Member] | Grade: 6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	314,458	209,844
Total Loans and Leases Held for Investment, Acquired	75,189	98,977
Real Estate-Commercial [Member] | Grade: 7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	31,791	12,974
Total Loans and Leases Held for Investment, Acquired	0	17,028
Real Estate-Commercial [Member] | Grade: 8. Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	20,554	23,834
Total Loans and Leases Held for Investment, Acquired	12,714	6,483
Real Estate-Commercial [Member] | Grade: 9. Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Commercial [Member] | Grade: 10. Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Commercial [Member] | Internally Assigned Grades [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	1,507,579	1,235,681
Total Loans and Leases Held for Investment, Acquired	233,625	306,460
Real Estate-Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	215,513	171,244
Total Loans and Leases Held for Investment, Acquired	0	4,592
Real Estate-Construction [Member] | Grade: 1. Cash secured/ 2. Fully secured [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	27,783	20,420
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Construction [Member] | Grade: 3. Strong [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Construction [Member] | Grade: 4. Satisfactory [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Construction [Member] | Grade: 5. Acceptable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	78,855	76,899
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Construction [Member] | Grade: 6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	108,769	72,168
Total Loans and Leases Held for Investment, Acquired	0	4,592
Real Estate-Construction [Member] | Grade: 7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	1,392
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Construction [Member] | Grade: 8. Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	106	365
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Construction [Member] | Grade: 9. Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Construction [Member] | Grade: 10. Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Construction [Member] | Internally Assigned Grades [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	215,513	171,244
Total Loans and Leases Held for Investment, Acquired	0	4,592
Real Estate-Residential Secured for Business Purpose [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	302,393	250,800
Total Loans and Leases Held for Investment, Acquired	60,403	91,167
Real Estate-Residential Secured for Business Purpose [Member] | Grade: 1. Cash secured/ 2. Fully secured [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Residential Secured for Business Purpose [Member] | Grade: 3. Strong [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Residential Secured for Business Purpose [Member] | Grade: 4. Satisfactory [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	274
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Residential Secured for Business Purpose [Member] | Grade: 5. Acceptable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	251,099	215,750
Total Loans and Leases Held for Investment, Acquired	51,066	73,402
Real Estate-Residential Secured for Business Purpose [Member] | Grade: 6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	47,257	29,738
Total Loans and Leases Held for Investment, Acquired	8,501	15,861
Real Estate-Residential Secured for Business Purpose [Member] | Grade: 7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	721	296
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Residential Secured for Business Purpose [Member] | Grade: 8. Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	3,316	4,742
Total Loans and Leases Held for Investment, Acquired	836	1,904
Real Estate-Residential Secured for Business Purpose [Member] | Grade: 9. Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Residential Secured for Business Purpose [Member] | Grade: 10. Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	0	0
Total Loans and Leases Held for Investment, Acquired	0	0
Real Estate-Residential Secured for Business Purpose [Member] | Internally Assigned Grades [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	302,393	250,800
Total Loans and Leases Held for Investment, Acquired	60,403	91,167
Real Estate-Residential Secured for Personal Purpose [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	338,451	260,654
Total Loans and Leases Held for Investment, Acquired	49,959	60,920
Real Estate-Residential Secured for Personal Purpose [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	337,762	260,589
Total Loans and Leases Held for Investment, Acquired	49,061	60,477
Real Estate-Residential Secured for Personal Purpose [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	689	65
Total Loans and Leases Held for Investment, Acquired	898	443
Real Estate-Residential Secured for Personal Purpose [Member] | Performing and Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	338,451	260,654
Total Loans and Leases Held for Investment, Acquired	49,959	60,920
Real Estate-Home Equity Secured for Personal Purpose [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	177,523	171,884
Total Loans and Leases Held for Investment, Acquired	8,728	12,386
Real Estate-Home Equity Secured for Personal Purpose [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	177,139	171,527
Total Loans and Leases Held for Investment, Acquired	7,664	12,084
Real Estate-Home Equity Secured for Personal Purpose [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	384	357
Total Loans and Leases Held for Investment, Acquired	1,064	302
Real Estate-Home Equity Secured for Personal Purpose [Member] | Performing and Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	177,523	171,884
Total Loans and Leases Held for Investment, Acquired	8,728	12,386
Loans to Individuals [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	32,617	28,156
Total Loans and Leases Held for Investment, Acquired	142	144
Loans to Individuals [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	32,562	27,961
Total Loans and Leases Held for Investment, Acquired	142	144
Loans to Individuals [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	55	195
Total Loans and Leases Held for Investment, Acquired	0	0
Loans to Individuals [Member] | Performing and Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	32,617	28,156
Total Loans and Leases Held for Investment, Acquired	142	144
Lease Financings [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	141,956	129,768
Total Loans and Leases Held for Investment, Acquired	0	0
Lease Financings [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	141,649	127,913
Total Loans and Leases Held for Investment, Acquired	0	0
Lease Financings [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	307	1,855
Total Loans and Leases Held for Investment, Acquired	0	0
Lease Financings [Member] | Performing and Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	141,956	129,768
Total Loans and Leases Held for Investment, Acquired	$ 0	$ 0