Loans - Summary of Carrying Balance of Troubled Debt Restructurings at Dates (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Modifications [Line Items]
Total troubled debt restructurings	$ 26,998	$ 33,278
Loans, Gross [Member]
Financing Receivable, Modifications [Line Items]
Total troubled debt restructurings	26,998	33,278
Other Loans Held for Sale [Member]
Financing Receivable, Modifications [Line Items]
Total troubled debt restructurings
Performing [Member]
Financing Receivable, Modifications [Line Items]
Total troubled debt restructurings	24,169	30,154
Performing [Member] | Loans, Gross [Member]
Financing Receivable, Modifications [Line Items]
Total troubled debt restructurings	24,169	30,154
Performing [Member] | Other Loans Held for Sale [Member]
Financing Receivable, Modifications [Line Items]
Total troubled debt restructurings
Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Total troubled debt restructurings	2,829	3,124
Nonperforming [Member] | Loans, Gross [Member]
Financing Receivable, Modifications [Line Items]
Total troubled debt restructurings	2,829	3,124
Nonperforming [Member] | Other Loans Held for Sale [Member]
Financing Receivable, Modifications [Line Items]
Total troubled debt restructurings