Loans and Leases - Credit Quality Indicators (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	$ 3,081,287	$ 2,390,832
Total Loans and Leases Held for Investment, Acquired	538,780	895,054
Grade: 1. Cash secured/ 2. Fully secured [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	22,941	14,148
Total Loans and Leases Held for Investment, Acquired	1,120	583
Grade: 3. Strong [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	11,027	17,025
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	57,507	74,757
Total Loans and Leases Held for Investment, Acquired	607	5,417
Grade: 5. Acceptable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	1,846,112	1,386,253
Total Loans and Leases Held for Investment, Acquired	306,841	533,598
Grade: 6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	491,740	272,383
Total Loans and Leases Held for Investment, Acquired	125,613	221,113
Grade: 7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	18,689	32,772
Total Loans and Leases Held for Investment, Acquired	18,035	14,023
Grade: 8. Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	42,809	70,286
Total Loans and Leases Held for Investment, Acquired	13,114	24,769
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	2,490,825	1,867,624
Total Loans and Leases Held for Investment, Acquired	465,330	799,503
Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	587,990	521,472
Total Loans and Leases Held for Investment, Acquired	72,705	94,679
Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	2,472	1,736
Total Loans and Leases Held for Investment, Acquired	745	872
Performing and Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	590,462	523,208
Total Loans and Leases Held for Investment, Acquired	73,450	95,551
Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	833,100	663,221
Total Loans and Leases Held for Investment, Acquired	63,111	160,045
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	2,521	272
Total Loans and Leases Held for Investment, Acquired	1,120	583
Commercial, Financial and Agricultural [Member] | Grade: 3. Strong [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	9,206	14,980
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	30,283	35,529
Total Loans and Leases Held for Investment, Acquired	125	4,399
Commercial, Financial and Agricultural [Member] | Grade: 5. Acceptable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	593,205	465,675
Total Loans and Leases Held for Investment, Acquired	49,949	113,512
Commercial, Financial and Agricultural [Member] | Grade: 6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	179,990	113,499
Total Loans and Leases Held for Investment, Acquired	6,183	31,697
Commercial, Financial and Agricultural [Member] | Grade: 7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	4,027	8,820
Total Loans and Leases Held for Investment, Acquired	1,007	73
Commercial, Financial and Agricultural [Member] | Grade: 8. Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	13,868	24,446
Total Loans and Leases Held for Investment, Acquired	4,727	9,781
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	833,100	663,221
Total Loans and Leases Held for Investment, Acquired	63,111	160,045
Real Estate-Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	1,235,681	909,581
Total Loans and Leases Held for Investment, Acquired	306,460	465,368
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	1,821	2,045
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	26,950	38,861
Total Loans and Leases Held for Investment, Acquired	482	1,018
Real Estate-Commercial [Member] | Grade: 5. Acceptable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	960,258	676,212
Total Loans and Leases Held for Investment, Acquired	183,490	282,199
Real Estate-Commercial [Member] | Grade: 6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	209,844	128,646
Total Loans and Leases Held for Investment, Acquired	98,977	163,623
Real Estate-Commercial [Member] | Grade: 7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	12,974	22,439
Total Loans and Leases Held for Investment, Acquired	17,028	7,705
Real Estate-Commercial [Member] | Grade: 8. Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	23,834	41,378
Total Loans and Leases Held for Investment, Acquired	6,483	10,823
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	1,235,681	909,581
Total Loans and Leases Held for Investment, Acquired	306,460	465,368
Real Estate-Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	171,244	142,891
Total Loans and Leases Held for Investment, Acquired	4,592	31,953
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	20,420	13,714
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	76,899	110,650
Total Loans and Leases Held for Investment, Acquired	0	20,565
Real Estate-Construction [Member] | Grade: 6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	72,168	18,213
Total Loans and Leases Held for Investment, Acquired	4,592	11,388
Real Estate-Construction [Member] | Grade: 7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	1,392	314
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	365	0
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	171,244	142,891
Total Loans and Leases Held for Investment, Acquired	4,592	31,953
Real Estate-Residential Secured for Business Purpose [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	250,800	151,931
Total Loans and Leases Held for Investment, Acquired	91,167	142,137
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	162
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	274	367
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	215,750	133,716
Total Loans and Leases Held for Investment, Acquired	73,402	117,322
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	29,738	12,025
Total Loans and Leases Held for Investment, Acquired	15,861	14,405
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	296	1,199
Total Loans and Leases Held for Investment, Acquired	0	6,245
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	4,742	4,462
Total Loans and Leases Held for Investment, Acquired	1,904	4,165
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	250,800	151,931
Total Loans and Leases Held for Investment, Acquired	91,167	142,137
Real Estate-Residential Secured for Personal Purpose [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	260,654	210,377
Total Loans and Leases Held for Investment, Acquired	60,920	80,431
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	260,589	210,208
Total Loans and Leases Held for Investment, Acquired	60,477	79,559
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	65	169
Total Loans and Leases Held for Investment, Acquired	443	872
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	260,654	210,377
Total Loans and Leases Held for Investment, Acquired	60,920	80,431
Real Estate-Home Equity Secured for Personal Purpose [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	171,884	147,982
Total Loans and Leases Held for Investment, Acquired	12,386	14,857
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	171,527	147,286
Total Loans and Leases Held for Investment, Acquired	12,084	14,857
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	357	696
Total Loans and Leases Held for Investment, Acquired	302	0
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	171,884	147,982
Total Loans and Leases Held for Investment, Acquired	12,386	14,857
Loans to Individuals [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	28,156	30,110
Total Loans and Leases Held for Investment, Acquired	144	263
Loans to Individuals [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	27,961	29,968
Total Loans and Leases Held for Investment, Acquired	144	263
Loans to Individuals [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	195	142
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	28,156	30,110
Total Loans and Leases Held for Investment, Acquired	144	263
Lease Financings [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases Held for Investment, Originated	129,768	134,739
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	127,913	134,010
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	1,855	729
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	129,768	134,739
Total Loans and Leases Held for Investment, Acquired	$ 0	$ 0