Loans and Allowance for Credit Losses - Schedule of Average Balance and Interest Income Recognized on Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment, Total	$ 71,028	$ 66,309	$ 71,878	$ 76,677
Interest Income Recognized	100	56	297	224
Commercial Loan [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	14,043	8,514	11,002	10,246
Interest Income Recognized with no related allowance	33	40	91	40
Average Recorded Investment with an allowance recorded	12,989	19,372	16,462	23,081
Interest Income Recognized with an allowance recorded	19	(10)	50	58
Commercial Real Estate-Construction [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	583	1,322	871	796
Interest Income Recognized with no related allowance		2		2
Average Recorded Investment with an allowance recorded	2,989	438	3,180	3,464
Interest Income Recognized with an allowance recorded		(2)
Commercial Real Estate-Other [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	13,868	13,417	15,600	16,349
Interest Income Recognized with no related allowance	44	27	57	70
Average Recorded Investment with an allowance recorded	26,556	23,246	24,763	22,741
Interest Income Recognized with an allowance recorded	$ 4	$ (1)	$ 99	$ 54