Allowance for Loan Losses - Presentation of Credit Quality Indicators (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 2,320,883	$ 2,282,524	$ 1,687,052
Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,675,713	1,612,749
PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	595,619	616,878
PCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	49,551	52,897
Pass [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,602,118	1,537,988
Pass [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	573,831	596,332
Special mention [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	20,269	18,836
Special mention [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	14,722	15,107
Substandard [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	53,326	55,925
Substandard [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	7,066	5,439
Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	40,105	38,618	37,394
Residential [Member] | Originated loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	23,664	21,135
Residential [Member] | PNCI loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	15,705	16,808
Residential [Member] | PCI loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	736	675
Residential [Member] | Pass [Member] | Originated loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	20,498	18,112
Residential [Member] | Pass [Member] | PNCI loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	15,705	16,808
Residential [Member] | Special mention [Member] | Originated loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	793	622
Residential [Member] | Substandard [Member] | Originated loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,373	2,401
Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	45,648	35,518	22,156
Commercial [Member] | Originated loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	32,558	24,545
Commercial [Member] | PNCI loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	13,090	11,973
Commercial [Member] | Pass [Member] | Originated loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	31,877	24,436
Commercial [Member] | Pass [Member] | PNCI loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	13,090	11,973
Commercial [Member] | Special mention [Member] | Originated loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	584
Commercial [Member] | Substandard [Member] | Originated loans [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	97	109
Home equity lines of credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	345,210	352,584	337,802
Home equity lines of credit [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	299,298	305,166
Home equity lines of credit [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	36,953	38,397
Home equity lines of credit [Member] | PCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	8,959	9,021
Home equity lines of credit [Member] | Pass [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	286,624	292,244
Home equity lines of credit [Member] | Pass [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	34,903	36,531
Home equity lines of credit [Member] | Special mention [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	3,641	3,590
Home equity lines of credit [Member] | Special mention [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	935	936
Home equity lines of credit [Member] | Substandard [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	9,033	9,332
Home equity lines of credit [Member] | Substandard [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,115	930
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	32,999	33,074	27,633
Other Consumer [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	28,740	28,230
Other Consumer [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	4,189	4,770
Other Consumer [Member] | PCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	70	74
Other Consumer [Member] | Pass [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	28,010	27,396
Other Consumer [Member] | Pass [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	3,914	4,399
Other Consumer [Member] | Special mention [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	487	591
Other Consumer [Member] | Special mention [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	123	230
Other Consumer [Member] | Substandard [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	243	243
Other Consumer [Member] | Substandard [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	152	141
RE Mortgage [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	282,383	279,420	195,826
RE Mortgage [Member] | Residential [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	160,041	154,594
RE Mortgage [Member] | Residential [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	118,316	120,821
RE Mortgage [Member] | Residential [Member] | PCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	4,026	4,005
RE Mortgage [Member] | Residential [Member] | Pass [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	152,273	146,949
RE Mortgage [Member] | Residential [Member] | Pass [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	116,888	119,643
RE Mortgage [Member] | Residential [Member] | Special mention [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,315	1,122
RE Mortgage [Member] | Residential [Member] | Special mention [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	680	547
RE Mortgage [Member] | Residential [Member] | Substandard [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	6,453	6,523
RE Mortgage [Member] | Residential [Member] | Substandard [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	748	631
RE Mortgage [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,364,480	1,335,939	930,472
RE Mortgage [Member] | Commercial [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	970,433	928,797
RE Mortgage [Member] | Commercial [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	366,096	376,225
RE Mortgage [Member] | Commercial [Member] | PCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	27,951	30,917
RE Mortgage [Member] | Commercial [Member] | Pass [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	926,236	883,102
RE Mortgage [Member] | Commercial [Member] | Pass [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	348,541	359,537
RE Mortgage [Member] | Commercial [Member] | Special mention [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	11,795	11,521
RE Mortgage [Member] | Commercial [Member] | Special mention [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	12,874	12,979
RE Mortgage [Member] | Commercial [Member] | Substandard [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	32,402	34,174
RE Mortgage [Member] | Commercial [Member] | Substandard [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	4,681	3,709
Home equity loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	32,486	31,314	15,776
Home equity loans [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	26,892	23,559
Home equity loans [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	4,841	6,985
Home equity loans [Member] | PCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	753	770
Home equity loans [Member] | Pass [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	24,010	20,976
Home equity loans [Member] | Pass [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	4,662	6,813
Home equity loans [Member] | Special mention [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	891	743
Home equity loans [Member] | Special mention [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	105	147
Home equity loans [Member] | Substandard [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,991	1,840
Home equity loans [Member] | Substandard [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	74	25
Auto Indirect [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	32	112	575
Auto Indirect [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	32	112
Auto Indirect [Member] | Pass [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		66
Auto Indirect [Member] | Special mention [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	6	11
Auto Indirect [Member] | Substandard [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	26	35
C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	177,540	174,945	119,418
C&I [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	134,055	126,611
C&I [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	36,429	40,899
C&I [Member] | PCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	7,056	7,435
C&I [Member] | Pass [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	132,590	124,707
C&I [Member] | Pass [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	36,128	40,628
C&I [Member] | Special mention [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	757	636
C&I [Member] | Special mention [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	5	268
C&I [Member] | Substandard [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	708	1,268
C&I [Member] | Substandard [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 296	$ 3