Allowance for Loan Losses - Analysis of Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 4,777	$ 10,172
Current	2,268,759	1,978,573
Total orig. loans	2,273,536	1,988,745
> 90 Days and still accruing	0	0
Nonaccrual loans	13,083	22,824
PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	533	8,924
Current	411,274	485,064
Total orig. loans	411,807	493,988
> 90 Days and still accruing	0	0
Nonaccrual loans	2,643	5,398
Home Equity Lines of Credit [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,218	1,877
Current	271,057	283,542
Total orig. loans	272,275	285,419
> 90 Days and still accruing	0	0
Nonaccrual loans	1,790	3,379
Home Equity Lines of Credit [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	139	367
Current	24,239	28,968
Total orig. loans	24,378	29,335
> 90 Days and still accruing	0	0
Nonaccrual loans	464	676
Other Consumer [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	90	71
Current	28,892	28,927
Total orig. loans	28,982	28,998
> 90 Days and still accruing	0	0
Nonaccrual loans	15	21
Other Consumer [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	19	23
Current	2,549	3,344
Total orig. loans	2,568	3,367
> 90 Days and still accruing	0	0
Nonaccrual loans	6	33
C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,521	2,221
Current	198,426	168,099
Total orig. loans	199,947	170,320
> 90 Days and still accruing	0	0
Nonaccrual loans	1,106	976
C&I [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		1
Current	13,015	19,743
Total orig. loans	13,015	19,744
> 90 Days and still accruing	0	0
30-59 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,569	4,635
30-59 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	117	7,259
30-59 Days [Member] | Home Equity Lines of Credit [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	599	1,033
30-59 Days [Member] | Home Equity Lines of Credit [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		92
30-59 Days [Member] | Other Consumer [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	64	12
30-59 Days [Member] | Other Consumer [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	19
30-59 Days [Member] | C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	890	2,197
30-59 Days [Member] | C&I [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		1
60-89 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	200	1,196
60-89 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	205	13
60-89 Days [Member] | Home Equity Lines of Credit [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	31	324
60-89 Days [Member] | Home Equity Lines of Credit [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	139
60-89 Days [Member] | Other Consumer [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	19	40
60-89 Days [Member] | Other Consumer [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		13
60-89 Days [Member] | C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	150
> 90 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,008	4,341
> 90 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	211	1,652
> 90 Days [Member] | Home Equity Lines of Credit [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	588	520
> 90 Days [Member] | Home Equity Lines of Credit [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		275
> 90 Days [Member] | Other Consumer [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	7	19
> 90 Days [Member] | Other Consumer [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		10
> 90 Days [Member] | C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	481	24
Home Equity Loans [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,144	825
Current	37,121	33,892
Total orig. loans	38,265	34,717
> 90 Days and still accruing	0	0
Nonaccrual loans	1,592	1,195
Home Equity Loans [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	155	94
Current	3,547	3,924
Total orig. loans	3,702	4,018
> 90 Days and still accruing	0	0
Nonaccrual loans	97	109
Home Equity Loans [Member] | 30-59 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	758	402
Home Equity Loans [Member] | 30-59 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	93	23
Home Equity Loans [Member] | 60-89 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		341
Home Equity Loans [Member] | > 90 Days [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	386	82
Home Equity Loans [Member] | > 90 Days [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	62	71
Auto Indirect [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
> 90 Days and still accruing	0	0
Auto Indirect [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
> 90 Days and still accruing	0	0
Construction [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	155
Current	57,048	31,778
Total orig. loans	57,203	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	146	13,636
Total orig. loans	146	13,636
> 90 Days and still accruing	0	0
Construction [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	52,370	66,285
Total orig. loans	52,370	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	8,925	7,999
Total orig. loans	8,925	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	155
Construction [Member] | > 90 Days [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		490
RE Mortgage [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	204	1,062
Current	224,975	206,523
Total orig. loans	225,179	207,585
> 90 Days and still accruing	0	0
Nonaccrual loans	1,520	3,045
RE Mortgage [Member] | Residential [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	140	3,164
Current	86,385	101,371
Total orig. loans	86,525	104,535
> 90 Days and still accruing	0	0
Nonaccrual loans	203	348
RE Mortgage [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	445	4,116
Current	1,398,870	1,159,527
Total orig. loans	1,399,315	1,163,643
> 90 Days and still accruing	0	0
Nonaccrual loans	7,049	14,196
RE Mortgage [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	80	4,785
Current	272,468	306,079
Total orig. loans	272,548	310,864
> 90 Days and still accruing	0	0
Nonaccrual loans	1,873	3,742
RE Mortgage [Member] | 30-59 Days [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	103	791
RE Mortgage [Member] | 30-59 Days [Member] | Residential [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5	3,106
RE Mortgage [Member] | 30-59 Days [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		200
RE Mortgage [Member] | 30-59 Days [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		4,037
RE Mortgage [Member] | 60-89 Days [Member] | Residential [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	66
RE Mortgage [Member] | 60-89 Days [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		491
RE Mortgage [Member] | > 90 Days [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	101	271
RE Mortgage [Member] | > 90 Days [Member] | Residential [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	69	58
RE Mortgage [Member] | > 90 Days [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	445	3,425
RE Mortgage [Member] | > 90 Days [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 80	$ 748