Loans and Allowance for Credit Losses - Schedule of Loans by Class Modified as Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013 SecurityLoan	Dec. 31, 2012 SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans	70	108
Pre-modification Outstanding Recorded Investment	$ 6,744	$ 28,377
Post-modification Outstanding Recorded Investment	6,469	28,222
Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	13	44
Pre-modification Outstanding Recorded Investment	2,212	9,585
Post-modification Outstanding Recorded Investment	2,172	9,574
Commercial Real Estate Construction Financing Receivable [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 Receivable [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	18	35
Pre-modification Outstanding Recorded Investment	3,456	16,404
Post-modification Outstanding Recorded Investment	3,307	16,272
Consumer - Other [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	39	26
Pre-modification Outstanding Recorded Investment	1,076	996
Post-modification Outstanding Recorded Investment	$ 990	$ 994