Loans and Allowance for Credit Losses - Schedule of Loans by Class Modified as Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013 SecurityLoan	Dec. 31, 2012 SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans	100	108
Pre-modification Outstanding Recorded Investment	$ 25,977	$ 28,377
Post-modification Outstanding Recorded Investment	24,062	28,222
Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	28	44
Pre-modification Outstanding Recorded Investment	14,272	9,585
Post-modification Outstanding Recorded Investment	13,238	9,574
Commercial Real Estate-Construction [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans		3
Pre-modification Outstanding Recorded Investment		1,392
Post-modification Outstanding Recorded Investment		1,382
Commercial Real Estate-Other [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	28	35
Pre-modification Outstanding Recorded Investment	9,741	16,404
Post-modification Outstanding Recorded Investment	8,961	16,272
Consumer - Other [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	44	26
Pre-modification Outstanding Recorded Investment	1,964	996
Post-modification Outstanding Recorded Investment	$ 1,863	$ 994