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
	Mar. 31, 2013 Contract	Mar. 31, 2012 Contract
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts	2	2
Recorded Investment	$ 16	$ 980
Real estate construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts	0	2
Recorded Investment	0	980
Loans to individuals [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Contracts	1	0
Recorded Investment	$ 6	$ 0