Allowance for Loan Losses - Analysis of Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 10,640	$ 9,129
Current	1,893,507	1,603,620
Total orig. loans	1,904,147	1,612,749
> 90 Days and still accruing	243
Nonaccrual loans	23,801	32,529
PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,095	3,226
Current	518,381	613,652
Total orig. loans	520,476	616,878
Nonaccrual loans	5,179	1,646
30-59 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,416	5,519
30-59 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	667	2,668
60-89 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,976	1,530
60-89 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	386	145
> 90 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,248	2,080
> 90 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,042	413
RE Mortgage [Member] | Residential [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,413	2,315
Current	190,213	152,279
Total orig. loans	191,626	154,594
Nonaccrual loans	3,866	3,430
RE Mortgage [Member] | Residential [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	471	2,304
Current	107,796	118,517
Total orig. loans	108,267	120,821
Nonaccrual loans	691	799
RE Mortgage [Member] | Residential [Member] | 30-59 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	128	1,296
RE Mortgage [Member] | Residential [Member] | 30-59 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		2,041
RE Mortgage [Member] | Residential [Member] | 60-89 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	624	919
RE Mortgage [Member] | Residential [Member] | 60-89 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	384	24
RE Mortgage [Member] | Residential [Member] | > 90 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	661	100
RE Mortgage [Member] | Residential [Member] | > 90 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	87	239
RE Mortgage [Member] | Commercial [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	4,877	1,635
Current	1,097,400	927,162
Total orig. loans	1,102,277	928,797
> 90 Days and still accruing	243
Nonaccrual loans	15,048	20,736
RE Mortgage [Member] | Commercial [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	676	260
Current	325,266	375,965
Total orig. loans	325,942	376,225
Nonaccrual loans	3,750	366
RE Mortgage [Member] | Commercial [Member] | 30-59 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	636	735
RE Mortgage [Member] | Commercial [Member] | 30-59 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		260
RE Mortgage [Member] | Commercial [Member] | 60-89 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	492
RE Mortgage [Member] | Commercial [Member] | > 90 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,749	900
RE Mortgage [Member] | Commercial [Member] | > 90 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	676
Home equity lines of credit [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,758	3,116
Current	289,049	302,050
Total orig. loans	291,807	305,166
Nonaccrual loans	3,328	4,336
Home equity lines of credit [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	374	466
Current	30,941	37,931
Total orig. loans	31,315	38,397
Nonaccrual loans	632	346
Home equity lines of credit [Member] | 30-59 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,815	2,066
Home equity lines of credit [Member] | 30-59 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	113	275
Home equity lines of credit [Member] | 60-89 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	402	296
Home equity lines of credit [Member] | 60-89 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		118
Home equity lines of credit [Member] | > 90 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	541	754
Home equity lines of credit [Member] | > 90 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	261	73
Home equity loans [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	793	1,009
Current	31,792	22,550
Total orig. loans	32,585	23,559
Nonaccrual loans	1,236	1,197
Home equity loans [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	44	25
Current	4,117	6,960
Total orig. loans	4,161	6,985
Nonaccrual loans	58	25
Home equity loans [Member] | 30-59 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	156	615
Home equity loans [Member] | 30-59 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	44
Home equity loans [Member] | 60-89 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	384	192
Home equity loans [Member] | > 90 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	253	202
Home equity loans [Member] | > 90 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		25
Auto Indirect [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		21
Current		91
Total orig. loans		112
Nonaccrual loans		18
Auto Indirect [Member] | 30-59 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		4
Auto Indirect [Member] | > 90 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due		17
Other Consumer [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	44	134
Current	29,403	28,096
Total orig. loans	29,447	28,230
Nonaccrual loans	27	66
Other Consumer [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	28	104
Current	3,488	4,666
Total orig. loans	3,516	4,770
Nonaccrual loans	43	110
Other Consumer [Member] | 30-59 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	10	64
Other Consumer [Member] | 30-59 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	8	25
Other Consumer [Member] | 60-89 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	14	24
Other Consumer [Member] | 60-89 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2	3
Other Consumer [Member] | > 90 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	20	46
Other Consumer [Member] | > 90 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	18	76
C&I [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	233	899
Current	172,481	125,712
Total orig. loans	172,714	126,611
Nonaccrual loans	179	246
C&I [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5	67
Current	21,618	40,832
Total orig. loans	21,623	40,899
Nonaccrual loans	5
C&I [Member] | 30-59 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	149	739
C&I [Member] | 30-59 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5	67
C&I [Member] | 60-89 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	60	99
C&I [Member] | > 90 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	24	61
Construction [Member] | Residential [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	522
Current	29,890	21,135
Total orig. loans	30,412	21,135
Nonaccrual loans	37	2,401
Construction [Member] | Residential [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	14,925	16,808
Total orig. loans	14,925	16,808
Construction [Member] | Residential [Member] | 30-59 Days [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	522
Construction [Member] | Commercial [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	53,279	24,545
Total orig. loans	53,279	24,545
Nonaccrual loans	80	99
Construction [Member] | Commercial [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	497
Current	10,230	11,973
Total orig. loans	10,727	$ 11,973
Construction [Member] | Commercial [Member] | 30-59 Days [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 497