Loans and Allowance for Credit Losses - Troubled Debt Restructured Loans and Commitments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Modifications, Recorded Investment	$ 31,330	$ 64,016
Loans and Leases Receivable, Impaired, Commitment to Lend	1,953	1,574
Letter of Credit [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Loans and Leases Receivable, Impaired, Commitment to Lend	0	1,574
Unused lines of Credit [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Loans and Leases Receivable, Impaired, Commitment to Lend	1,953	0
Non Accrual Loans [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Modifications, Recorded Investment	13,811	13,037
Non Accrual Loans [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Modifications, Recorded Investment	$ 17,519	$ 50,979