Loans and Allowance for Credit Losses - Troubled Debt Restructured Loans and Commitments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Modifications, Recorded Investment	$ 17,947	$ 30,475
Loans and Leases Receivable, Impaired, Commitment to Lend	974	452
Letter of Credit [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Loans and Leases Receivable, Impaired, Commitment to Lend	0	0
Unused lines of Credit [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Loans and Leases Receivable, Impaired, Commitment to Lend	974	452
Non Accrual Loans [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Modifications, Recorded Investment	11,164	13,495
Non Accrual Loans [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Financing Receivable, Modifications, Recorded Investment	$ 6,783	$ 16,980