Loans - Summary of Loans Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 Contract	Mar. 31, 2012 Contract
Financing Receivable, Recorded Investment [Line Items]
Number of loans		4
Recorded investment		$ 1,185
Nonfarm nonresidential [Member]
Financing Receivable, Recorded Investment [Line Items]
Number of loans		3
Recorded investment		1,139
Single-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Number of loans		1
Recorded investment		46
Other Loans Held for Sale [Member]
Financing Receivable, Recorded Investment [Line Items]
Number of loans
Recorded investment
Loans, Gross [Member]
Financing Receivable, Recorded Investment [Line Items]
Number of loans		4
Recorded investment		$ 1,185