Loans - Summary of Company's Internal Credit Quality Indicators Commercial and Industrial (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Commercial and industrial	$ 49,620	$ 51,661
Grade 1 [Member]
Financing Receivable, Recorded Investment [Line Items]
Commercial and industrial	2,195	3,462
Grade 2 [Member]
Financing Receivable, Recorded Investment [Line Items]
Commercial and industrial	149	208
Grade 3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Commercial and industrial	8,252	7,210
Grade 4 [Member]
Financing Receivable, Recorded Investment [Line Items]
Commercial and industrial	29,943	28,293
Grade W [Member]
Financing Receivable, Recorded Investment [Line Items]
Commercial and industrial	4,409	7,330
Grade 5 [Member]
Financing Receivable, Recorded Investment [Line Items]
Commercial and industrial	632	677
Grade 6 [Member]
Financing Receivable, Recorded Investment [Line Items]
Commercial and industrial	3,241	3,701
Grade 7 [Member]
Financing Receivable, Recorded Investment [Line Items]
Commercial and industrial	725	732
Not risk rated [Member]
Financing Receivable, Recorded Investment [Line Items]
Commercial and industrial	$ 74	$ 48