Loans and Allowance for Credit Losses - Troubled Debt Restructuring is 90 Days or More Past Due (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013 Contract	Sep. 30, 2012 Contract	Sep. 30, 2013 Contract	Sep. 30, 2012 Contract
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts	2	0	3	0
Recorded Investment	$ 14	$ 0	$ 18	$ 0
Residential real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts		0		0
Recorded Investment	9	0	9	0
Financing Receivable, Modification, Subsequent Default, Number of Contracts	1		1
Loans to individuals [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts		0		0
Recorded Investment	$ 5	$ 0	$ 9	$ 0
Financing Receivable, Modification, Subsequent Default, Number of Contracts	1		2