Allowance for Loan Losses - Analysis of Past Due and Nonaccrual Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	$ 3,924	$ 5,519
60-89 Days	1,315	1,530
> 90 Days	2,709	2,080
Total past due	7,948	9,129
Current	1,667,765	1,603,620
Total orig. loans	1,675,713	1,612,749
> 90 Days and still accruing	328
Nonaccrual loans	34,248	32,529
PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	2,058	2,668
60-89 Days	514	145
> 90 Days	215	413
Total past due	2,787	3,226
Current	592,832	613,652
Total orig. loans	595,619	616,878
Nonaccrual loans	2,236	1,646
RE Mortgage [Member] | Residential [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	1,225	1,296
60-89 Days		919
> 90 Days	629	100
Total past due	1,854	2,315
Current	158,187	152,279
Total orig. loans	160,041	154,594
> 90 Days and still accruing	328
Nonaccrual loans	4,111	3,430
RE Mortgage [Member] | Residential [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	1,401	2,041
60-89 Days		24
> 90 Days	121	239
Total past due	1,522	2,304
Current	116,832	118,517
Total orig. loans	118,354	120,821
Nonaccrual loans	728	799
RE Mortgage [Member] | Commercial [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	545	735
60-89 Days	714
> 90 Days	1,028	900
Total past due	2,287	1,635
Current	968,146	927,162
Total orig. loans	970,433	928,797
Nonaccrual loans	22,486	20,736
RE Mortgage [Member] | Commercial [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	560	260
60-89 Days	75
Total past due	635	260
Current	365,461	375,965
Total orig. loans	366,096	376,225
Nonaccrual loans	1,003	366
Home equity lines of credit [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	1,689	2,066
60-89 Days	285	296
> 90 Days	565	754
Total past due	2,539	3,116
Current	296,759	302,050
Total orig. loans	299,298	305,166
Nonaccrual loans	3,700	4,336
Home equity lines of credit [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	69	275
60-89 Days	395	118
> 90 Days	38	73
Total past due	502	466
Current	36,220	37,931
Total orig. loans	36,722	38,397
Nonaccrual loans	414	346
Home equity loans [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	140	615
60-89 Days	276	192
> 90 Days	390	202
Total past due	806	1,009
Current	26,086	22,550
Total orig. loans	26,892	23,559
Nonaccrual loans	1,217	1,197
Home equity loans [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
60-89 Days	43
> 90 Days	25	25
Total past due	68	25
Current	4,966	6,960
Total orig. loans	5,034	6,985
Nonaccrual loans	25	25
Auto Indirect [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	2	4
> 90 Days	14	17
Total past due	16	21
Current	16	91
Total orig. loans	32	112
Nonaccrual loans	14	18
Other Consumer [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	5	64
60-89 Days	5	24
> 90 Days	59	46
Total past due	69	134
Current	28,671	28,096
Total orig. loans	28,740	28,230
Nonaccrual loans	62	66
Other Consumer [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	28	25
60-89 Days	1	3
> 90 Days	31	76
Total past due	60	104
Current	4,129	4,666
Total orig. loans	4,189	4,770
Nonaccrual loans	66	110
C&I [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days	318	739
60-89 Days	35	99
> 90 Days	24	61
Total past due	377	899
Current	133,678	125,712
Total orig. loans	134,055	126,611
Nonaccrual loans	191	246
C&I [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due: 30-59 Days		67
Total past due		67
Current	36,429	40,832
Total orig. loans	36,429	40,899
Construction [Member] | Residential [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	23,664	21,135
Total orig. loans	23,664	21,135
Nonaccrual loans	2,373	2,401
Construction [Member] | Residential [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	15,705	16,808
Total orig. loans	15,705	16,808
Construction [Member] | Commercial [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	32,558	24,545
Total orig. loans	32,558	24,545
Nonaccrual loans	94	99
Construction [Member] | Commercial [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	13,090	11,973
Total orig. loans	$ 13,090	$ 11,973