Allowance for Loan Losses - Analysis of Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 8,687	$ 10,172
Current	2,347,640	1,978,573
Total orig. loans	2,356,327	1,988,745
> 90 Days and still accruing	0	0
Nonaccrual loans	12,894	22,824
PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,600	8,924
Current	375,622	485,064
Total orig. loans	378,222	493,988
> 90 Days and still accruing	0	0
Nonaccrual loans	2,834	5,398
30-59 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	4,354	4,635
30-59 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,896	7,259
60-89 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,586	1,196
60-89 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		13
> 90 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,747	4,341
> 90 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	704	1,652
Mortgage Loans on Real Estate [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	691	1,062
Current	228,918	206,523
Total orig. loans	229,609	207,585
> 90 Days and still accruing	0	0
Nonaccrual loans	255	3,045
Mortgage Loans on Real Estate [Member] | Residential [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,531	3,164
Current	77,404	101,371
Total orig. loans	78,935	104,535
> 90 Days and still accruing	0	0
Nonaccrual loans	194	348
Mortgage Loans on Real Estate [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,050	4,116
Current	1,482,370	1,159,527
Total orig. loans	1,484,420	1,163,643
> 90 Days and still accruing	0	0
Nonaccrual loans	7,736	14,196
Mortgage Loans on Real Estate [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	154	4,785
Current	249,883	306,079
Total orig. loans	250,037	310,864
> 90 Days and still accruing	0	0
Nonaccrual loans	1,826	3,742
Mortgage Loans on Real Estate [Member] | 30-59 Days [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	552	791
Mortgage Loans on Real Estate [Member] | 30-59 Days [Member] | Residential [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,510	3,106
Mortgage Loans on Real Estate [Member] | 30-59 Days [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	317	200
Mortgage Loans on Real Estate [Member] | 30-59 Days [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	73	4,037
Mortgage Loans on Real Estate [Member] | 60-89 Days [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	139
Mortgage Loans on Real Estate [Member] | 60-89 Days [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,517	491
Mortgage Loans on Real Estate [Member] | > 90 Days [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		271
Mortgage Loans on Real Estate [Member] | > 90 Days [Member] | Residential [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	21	58
Mortgage Loans on Real Estate [Member] | > 90 Days [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	216	3,425
Mortgage Loans on Real Estate [Member] | > 90 Days [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	81	748
Consumer [Member] | Home Equity Lines of Credit [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,441	1,877
Current	262,149	283,542
Total orig. loans	263,590	285,419
> 90 Days and still accruing	0	0
Nonaccrual loans	1,211	3,379
Consumer [Member] | Home Equity Lines of Credit [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	863	367
Current	20,902	28,968
Total orig. loans	21,765	29,335
> 90 Days and still accruing	0	0
Nonaccrual loans	742	676
Consumer [Member] | 30-59 Days [Member] | Home Equity Lines of Credit [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	754	1,033
Consumer [Member] | 30-59 Days [Member] | Home Equity Lines of Credit [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	274	92
Consumer [Member] | 60-89 Days [Member] | Home Equity Lines of Credit [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		324
Consumer [Member] | > 90 Days [Member] | Home Equity Lines of Credit [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	687	520
Consumer [Member] | > 90 Days [Member] | Home Equity Lines of Credit [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	589	275
Consumer [Member] | Home Equity Loans [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,225	825
Current	35,849	33,892
Total orig. loans	37,074	34,717
> 90 Days and still accruing	0	0
Nonaccrual loans	718	1,195
Consumer [Member] | Home Equity Loans [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	52	94
Current	3,566	3,924
Total orig. loans	3,618	4,018
> 90 Days and still accruing	0	0
Nonaccrual loans	67	109
Consumer [Member] | Home Equity Loans [Member] | 30-59 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	646	402
Consumer [Member] | Home Equity Loans [Member] | 30-59 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	39	23
Consumer [Member] | Home Equity Loans [Member] | 60-89 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	395	341
Consumer [Member] | Home Equity Loans [Member] | > 90 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	184	82
Consumer [Member] | Home Equity Loans [Member] | > 90 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	13	71
Consumer [Member] | Auto Indirect [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
> 90 Days and still accruing	0	0
Consumer [Member] | Auto Indirect [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
> 90 Days and still accruing	0	0
Consumer [Member] | Other Consumer [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	61	71
Current	28,106	28,927
Total orig. loans	28,167	28,998
> 90 Days and still accruing	0	0
Nonaccrual loans	33	21
Consumer [Member] | Other Consumer [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		23
Current	2,534	3,344
Total orig. loans	2,534	3,367
> 90 Days and still accruing	0	0
Nonaccrual loans	5	33
Consumer [Member] | Other Consumer [Member] | 30-59 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	16	12
Consumer [Member] | Other Consumer [Member] | 60-89 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	30	40
Consumer [Member] | Other Consumer [Member] | 60-89 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		13
Consumer [Member] | Other Consumer [Member] | > 90 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	15	19
Consumer [Member] | Other Consumer [Member] | > 90 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		10
Consumer and Industrial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,866	2,221
Current	198,869	168,099
Total orig. loans	200,735	170,320
> 90 Days and still accruing	0	0
Nonaccrual loans	2,930	976
Consumer and Industrial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		1
Current	12,321	19,743
Total orig. loans	12,321	19,744
> 90 Days and still accruing	0	0
Consumer and Industrial [Member] | 30-59 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,148	2,197
Consumer and Industrial [Member] | 30-59 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		1
Consumer and Industrial [Member] | 60-89 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	84
Consumer and Industrial [Member] | > 90 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	634	24
Construction [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	932
Current	53,681
Total orig. loans	54,613	31,778
> 90 Days and still accruing	0	0
Nonaccrual loans	11	12
Construction [Member] | Residential [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	141	13,636
Total orig. loans	141	13,636
> 90 Days and still accruing	0	0
Construction [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	421
Current	57,698
Total orig. loans	58,119	66,285
> 90 Days and still accruing	0	0
Construction [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		490
Current	8,871	7,999
Total orig. loans	8,871	8,489
> 90 Days and still accruing	0	0
Nonaccrual loans		490
Construction [Member] | 30-59 Days [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	921
Construction [Member] | 60-89 Days [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	421
Construction [Member] | > 90 Days [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 11
Construction [Member] | > 90 Days [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		$ 490