Loans and Allowance for Credit Losses - Schedule of Impaired Loans that are Individually Evaluated (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Recorded Investment, Total commercial and CRE	$ 66,513	$ 77,237
Unpaid Principal Balance, Total commercial and CRE	76,149	94,262
Related Allowance	6,531	7,492
Commercial Loan [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment with no related allowance	15,439	6,563
Unpaid Principal Balance with no related allowance	15,795	9,280
Recorded Investment with related allowance	9,506	23,417
Unpaid Principal Balance with related allowance	13,442	28,574
Related Allowance	3,959	4,702
Commercial Real Estate-Construction [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment with no related allowance	563	1,179
Unpaid Principal Balance with no related allowance	671	1,287
Recorded Investment with related allowance	3,133	3,227
Unpaid Principal Balance with related allowance	3,133	3,227
Related Allowance	69	69
Commercial Real Estate-Other [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment with no related allowance	14,255	16,944
Unpaid Principal Balance with no related allowance	18,089	23,162
Recorded Investment with related allowance	23,617	25,907
Unpaid Principal Balance with related allowance	25,019	28,732
Related Allowance	$ 2,503	$ 2,721