Loans and Allowance for Loan Losses - Summary of Recorded Investment Based on Delinquency Status (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	$ 885,715	$ 843,088	$ 830,312
Commercial Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	448,432	402,037
Total loans internally credit risk graded	491,329	465,481
Total loans not internally credit risk graded	394,386	377,607
Total ending loans balance	885,715
Commercial Credit Exposure [Member] | Grade 1-Minimal [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	114	3,157
Commercial Credit Exposure [Member] | Grade 2-Modest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Commercial Credit Exposure [Member] | Grade 3-Better than average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	1,561	1,621
Commercial Credit Exposure [Member] | Grade 4-Average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	38,188	50,086
Commercial Credit Exposure [Member] | Grade 5-Acceptable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	408,569	347,173
Commercial Credit Exposure [Member] | Grade 6-Special mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	9,482	19,494
Commercial Credit Exposure [Member] | Grade 7-Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	33,415	43,950
Commercial Credit Exposure [Member] | Grade 8-Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Commercial Credit Exposure [Member] | Grade 9-Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Commercial Credit Exposure [Member] | 1-29 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	386,533	368,599
Commercial Credit Exposure [Member] | 30-59 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	2,447	3,282
Commercial Credit Exposure [Member] | 60-89 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	1,791	1,436
Commercial Credit Exposure [Member] | 90 days and more Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	3,615	4,290
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	411,924	381,852	386,891
Commercial Real Estate [Member] | Commercial Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	374,055	324,587
Total loans internally credit risk graded	411,924	381,852
Total loans not internally credit risk graded
Total ending loans balance	411,924
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 1-Minimal [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 2-Modest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 3-Better than average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	1,551	1,602
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 4-Average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	33,278	44,527
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 5-Acceptable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	339,226	278,458
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 6-Special mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	6,415	16,390
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 7-Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	31,454	40,875
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 8-Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 9-Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | 1-29 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | 30-59 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | 60-89 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded
Commercial Real Estate [Member] | Commercial Credit Exposure [Member] | 90 days and more Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	71,922	76,570	72,679
Commercial [Member] | Commercial Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	68,415	72,378
Total loans internally credit risk graded	71,922	76,570
Total loans not internally credit risk graded
Total ending loans balance	71,922
Commercial [Member] | Commercial Credit Exposure [Member] | Grade 1-Minimal [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	114	3,157
Commercial [Member] | Commercial Credit Exposure [Member] | Grade 2-Modest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Commercial [Member] | Commercial Credit Exposure [Member] | Grade 3-Better than average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	10	19
Commercial [Member] | Commercial Credit Exposure [Member] | Grade 4-Average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	4,681	5,322
Commercial [Member] | Commercial Credit Exposure [Member] | Grade 5-Acceptable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	63,610	63,880
Commercial [Member] | Commercial Credit Exposure [Member] | Grade 6-Special mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	3,023	2,947
Commercial [Member] | Commercial Credit Exposure [Member] | Grade 7-Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	484	1,245
Commercial [Member] | Commercial Credit Exposure [Member] | Grade 8-Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Commercial [Member] | Commercial Credit Exposure [Member] | Grade 9-Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Commercial [Member] | Commercial Credit Exposure [Member] | 1-29 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded
Commercial [Member] | Commercial Credit Exposure [Member] | 30-59 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded
Commercial [Member] | Commercial Credit Exposure [Member] | 60-89 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded
Commercial [Member] | Commercial Credit Exposure [Member] | 90 days and more Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	68,549	64,524	68,837
Residential Real Estate [Member] | Commercial Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	5,962	5,072
Total loans internally credit risk graded	7,483	7,059
Total loans not internally credit risk graded	61,066	57,465
Total ending loans balance	68,549
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 1-Minimal [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 2-Modest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 3-Better than average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 4-Average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	229	237
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 5-Acceptable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	5,733	4,835
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 6-Special mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	44	157
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 7-Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	1,477	1,830
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 8-Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | Grade 9-Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | 1-29 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	57,545	53,276
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | 30-59 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	538	545
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | 60-89 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	1,218	1,172
Residential Real Estate [Member] | Commercial Credit Exposure [Member] | 90 days and more Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	1,765	2,472
Home Equity Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	125,108	126,958	130,143
Home Equity Loans [Member] | Commercial Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Total loans internally credit risk graded
Total loans not internally credit risk graded	125,108	126,958
Total ending loans balance	125,108
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | Grade 1-Minimal [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | Grade 2-Modest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | Grade 3-Better than average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | Grade 4-Average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | Grade 5-Acceptable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | Grade 6-Special mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | Grade 7-Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | Grade 8-Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | Grade 9-Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | 1-29 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	121,908	123,169
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | 30-59 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	1,191	1,942
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | 60-89 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	378	181
Home Equity Loans [Member] | Commercial Credit Exposure [Member] | 90 days and more Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	1,631	1,666
Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	195,358	180,089	158,885
Indirect [Member] | Commercial Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Total loans internally credit risk graded
Total loans not internally credit risk graded	195,358	180,089
Total ending loans balance	195,358
Indirect [Member] | Commercial Credit Exposure [Member] | Grade 1-Minimal [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Indirect [Member] | Commercial Credit Exposure [Member] | Grade 2-Modest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Indirect [Member] | Commercial Credit Exposure [Member] | Grade 3-Better than average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Indirect [Member] | Commercial Credit Exposure [Member] | Grade 4-Average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Indirect [Member] | Commercial Credit Exposure [Member] | Grade 5-Acceptable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Indirect [Member] | Commercial Credit Exposure [Member] | Grade 6-Special mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Indirect [Member] | Commercial Credit Exposure [Member] | Grade 7-Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Indirect [Member] | Commercial Credit Exposure [Member] | Grade 8-Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Indirect [Member] | Commercial Credit Exposure [Member] | Grade 9-Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Indirect [Member] | Commercial Credit Exposure [Member] | 1-29 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	194,499	179,230
Indirect [Member] | Commercial Credit Exposure [Member] | 30-59 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	657	664
Indirect [Member] | Commercial Credit Exposure [Member] | 60-89 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	146	71
Indirect [Member] | Commercial Credit Exposure [Member] | 90 days and more Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	56	124
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	12,854	13,095	12,877
Consumer [Member] | Commercial Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Total loans internally credit risk graded
Total loans not internally credit risk graded	12,854	13,095
Total ending loans balance	12,854
Consumer [Member] | Commercial Credit Exposure [Member] | Grade 1-Minimal [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Consumer [Member] | Commercial Credit Exposure [Member] | Grade 2-Modest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Consumer [Member] | Commercial Credit Exposure [Member] | Grade 3-Better than average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Consumer [Member] | Commercial Credit Exposure [Member] | Grade 4-Average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Consumer [Member] | Commercial Credit Exposure [Member] | Grade 5-Acceptable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits
Consumer [Member] | Commercial Credit Exposure [Member] | Grade 6-Special mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Consumer [Member] | Commercial Credit Exposure [Member] | Grade 7-Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Consumer [Member] | Commercial Credit Exposure [Member] | Grade 8-Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Consumer [Member] | Commercial Credit Exposure [Member] | Grade 9-Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded
Consumer [Member] | Commercial Credit Exposure [Member] | 1-29 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	12,581	12,924
Consumer [Member] | Commercial Credit Exposure [Member] | 30-59 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	61	131
Consumer [Member] | Commercial Credit Exposure [Member] | 60-89 days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	49	12
Consumer [Member] | Commercial Credit Exposure [Member] | 90 days and more Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	$ 163	$ 28