Summary of Interest Recognized and Cash-Basis Interest Earned on Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Average of individually impaired loans during period	$ 3,554	$ 3,554	$ 2,979
Interest income recognized during impairment	24	42	100
Cash-basis interest income recognized	$ 42	$ 110