Loans and Allowance for Loan Losses - Summary of Recorded Investment Based on Delinquency Status (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	$ 882,548		$ 843,088		$ 812,579
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	414,005		381,852		375,803
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	68,705		76,570		65,662
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	64,983		64,524		74,685
Home Equity Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	122,830		126,958		132,536
Indirect
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	199,924		180,089		150,031
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total ending loans balance	12,101		13,095		13,862
Commercial Credit Exposure
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	444,671		402,037
Total loans internally credit risk graded	(490,430)		(465,481)
Total loans not internally credit risk graded	(392,118)		(377,607)
Total ending loans balance	882,548		843,088
Commercial Credit Exposure | Grade 1-Minimal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	114		3,157
Commercial Credit Exposure | Grade 2-Modest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Grade 3-Better than average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	1,106		1,621
Commercial Credit Exposure | Grade 4-Average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	35,777		50,086
Commercial Credit Exposure | Grade 5-Acceptable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	407,674		347,173
Commercial Credit Exposure | Grade 6-Special mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	(15,637)		(19,494)
Commercial Credit Exposure | Grade 7-Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	(29,357)		(43,950)
Commercial Credit Exposure | Grade 8-Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	(765)		0
Commercial Credit Exposure | Grade 9-Loss
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Current loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(385,507)		(368,599)
Commercial Credit Exposure | 30-59 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(1,695)		(3,282)
Commercial Credit Exposure | 60-89 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(1,855)		(1,436)
Commercial Credit Exposure | 90 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(3,061)		(4,290)
Commercial Credit Exposure | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	373,771		324,587
Total loans internally credit risk graded	(414,005)		(381,852)
Total loans not internally credit risk graded	0		0
Total ending loans balance	414,005		381,852
Commercial Credit Exposure | Commercial Real Estate | Grade 1-Minimal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Commercial Real Estate | Grade 2-Modest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Commercial Real Estate | Grade 3-Better than average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	1,100		1,602
Commercial Credit Exposure | Commercial Real Estate | Grade 4-Average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	30,604		44,527
Commercial Credit Exposure | Commercial Real Estate | Grade 5-Acceptable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	342,067		278,458
Commercial Credit Exposure | Commercial Real Estate | Grade 6-Special mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	(12,201)		(16,390)
Commercial Credit Exposure | Commercial Real Estate | Grade 7-Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	(27,268)		(40,875)
Commercial Credit Exposure | Commercial Real Estate | Grade 8-Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	(765)		0
Commercial Credit Exposure | Commercial Real Estate | Grade 9-Loss
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Commercial Real Estate | Current loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	0		0
Commercial Credit Exposure | Commercial Real Estate | 30-59 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	0		0
Commercial Credit Exposure | Commercial Real Estate | 60-89 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	0		0
Commercial Credit Exposure | Commercial Real Estate | 90 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	0		0
Commercial Credit Exposure | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	64,690		72,378
Total loans internally credit risk graded	(68,705)		(76,570)
Total loans not internally credit risk graded	0		0
Total ending loans balance	68,705		76,570
Commercial Credit Exposure | Commercial | Grade 1-Minimal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	114		3,157
Commercial Credit Exposure | Commercial | Grade 2-Modest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Commercial | Grade 3-Better than average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	6		19
Commercial Credit Exposure | Commercial | Grade 4-Average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	4,547		5,322
Commercial Credit Exposure | Commercial | Grade 5-Acceptable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	60,023		63,880
Commercial Credit Exposure | Commercial | Grade 6-Special mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	(3,394)		(2,947)
Commercial Credit Exposure | Commercial | Grade 7-Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	(621)		(1,245)
Commercial Credit Exposure | Commercial | Grade 8-Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Commercial | Grade 9-Loss
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Commercial | Current loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	0		0
Commercial Credit Exposure | Commercial | 30-59 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	0		0
Commercial Credit Exposure | Commercial | 60-89 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	0		0
Commercial Credit Exposure | Commercial | 90 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	0		0
Commercial Credit Exposure | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	6,210	[1]	5,072	[1]
Total loans internally credit risk graded	(7,720)	[1]	(7,059)	[1]
Total loans not internally credit risk graded	(57,263)	[1]	(57,465)	[1]
Total ending loans balance	64,983	[1]	64,524	[1]
Commercial Credit Exposure | Residential Real Estate | Grade 1-Minimal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0	[1]	0	[1]
Commercial Credit Exposure | Residential Real Estate | Grade 2-Modest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0	[1]	0	[1]
Commercial Credit Exposure | Residential Real Estate | Grade 3-Better than average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0	[1]	0	[1]
Commercial Credit Exposure | Residential Real Estate | Grade 4-Average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	626	[1]	237	[1]
Commercial Credit Exposure | Residential Real Estate | Grade 5-Acceptable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	5,584	[1]	4,835	[1]
Commercial Credit Exposure | Residential Real Estate | Grade 6-Special mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	42	[1]	157	[1]
Commercial Credit Exposure | Residential Real Estate | Grade 7-Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	(1,468)	[1]	(1,830)	[1]
Commercial Credit Exposure | Residential Real Estate | Grade 8-Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0	[1]	0	[1]
Commercial Credit Exposure | Residential Real Estate | Grade 9-Loss
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0	[1]	0	[1]
Commercial Credit Exposure | Residential Real Estate | Current loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(54,416)	[1]	(53,276)	[1]
Commercial Credit Exposure | Residential Real Estate | 30-59 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(394)	[1]	(545)	[1]
Commercial Credit Exposure | Residential Real Estate | 60-89 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(1,094)	[1]	(1,172)	[1]
Commercial Credit Exposure | Residential Real Estate | 90 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(1,359)	[1]	(2,472)	[1]
Commercial Credit Exposure | Home Equity Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Total loans internally credit risk graded	0		0
Total loans not internally credit risk graded	(122,830)		(126,958)
Total ending loans balance	122,830		126,958
Commercial Credit Exposure | Home Equity Loans | Grade 1-Minimal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Home Equity Loans | Grade 2-Modest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Home Equity Loans | Grade 3-Better than average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Home Equity Loans | Grade 4-Average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Home Equity Loans | Grade 5-Acceptable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Home Equity Loans | Grade 6-Special mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Home Equity Loans | Grade 7-Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Home Equity Loans | Grade 8-Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Home Equity Loans | Grade 9-Loss
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Home Equity Loans | Current loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(120,196)		(123,169)
Commercial Credit Exposure | Home Equity Loans | 30-59 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(630)		(1,942)
Commercial Credit Exposure | Home Equity Loans | 60-89 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(494)		(181)
Commercial Credit Exposure | Home Equity Loans | 90 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(1,510)		(1,666)
Commercial Credit Exposure | Indirect
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Total loans internally credit risk graded	0		0
Total loans not internally credit risk graded	(199,924)		(180,089)
Total ending loans balance	199,924		180,089
Commercial Credit Exposure | Indirect | Grade 1-Minimal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Indirect | Grade 2-Modest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Indirect | Grade 3-Better than average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Indirect | Grade 4-Average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Indirect | Grade 5-Acceptable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Indirect | Grade 6-Special mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Indirect | Grade 7-Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Indirect | Grade 8-Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Indirect | Grade 9-Loss
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Indirect | Current loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(198,983)		(179,230)
Commercial Credit Exposure | Indirect | 30-59 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(645)		(664)
Commercial Credit Exposure | Indirect | 60-89 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(227)		(71)
Commercial Credit Exposure | Indirect | 90 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(69)		(124)
Commercial Credit Exposure | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Total loans internally credit risk graded	0		0
Total loans not internally credit risk graded	(12,101)		(13,095)
Total ending loans balance	12,101		13,095
Commercial Credit Exposure | Consumer | Grade 1-Minimal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Consumer | Grade 2-Modest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Consumer | Grade 3-Better than average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Consumer | Grade 4-Average
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Consumer | Grade 5-Acceptable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Pass Credits	0		0
Commercial Credit Exposure | Consumer | Grade 6-Special mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Consumer | Grade 7-Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Consumer | Grade 8-Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Consumer | Grade 9-Loss
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans internally credit risk graded	0		0
Commercial Credit Exposure | Consumer | Current loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(11,912)		(12,924)
Commercial Credit Exposure | Consumer | 30-59 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	(26)		(131)
Commercial Credit Exposure | Consumer | 60-89 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	40		12
Commercial Credit Exposure | Consumer | 90 days past due loans not internally risk graded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans not internally credit risk graded	$ (123)		$ (28)

[1] Residential loans with an internal commercial credit risk grade include loans that are secured by non owner occupied 1-4 family residential properties and conventional 1-4 family residential properties.