Loans and Allowance for Credit Losses - Schedule of Risk Category of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	$ 1,381,216	$ 1,336,820
Commercial Loan [Member] | Pass [Member]
Risk Category Of Loans [Line Items]
Total	1,238,695	1,237,274
Commercial Loan [Member] | Grade Criticized [Member]
Risk Category Of Loans [Line Items]
Total	92,893	38,476
Commercial Loan [Member] | Substandard [Member]
Risk Category Of Loans [Line Items]
Total	22,591	23,388
Commercial Loan [Member] | Doubtful [Member]
Risk Category Of Loans [Line Items]
Total	27,037	37,682
Commercial Real Estate-Construction [Member]
Risk Category Of Loans [Line Items]
Total	83,205	99,081
Commercial Real Estate-Construction [Member] | Pass [Member]
Risk Category Of Loans [Line Items]
Total	64,874	62,604
Commercial Real Estate-Construction [Member] | Grade Criticized [Member]
Risk Category Of Loans [Line Items]
Total	9,383	11,969
Commercial Real Estate-Construction [Member] | Substandard [Member]
Risk Category Of Loans [Line Items]
Total	2,579	10,204
Commercial Real Estate-Construction [Member] | Doubtful [Member]
Risk Category Of Loans [Line Items]
Total	6,369	14,304
Commercial Real Estate-Other [Member]
Risk Category Of Loans [Line Items]
Total	1,082,561	1,156,802
Commercial Real Estate-Other [Member] | Pass [Member]
Risk Category Of Loans [Line Items]
Total	952,765	965,967
Commercial Real Estate-Other [Member] | Grade Criticized [Member]
Risk Category Of Loans [Line Items]
Total	27,185	62,819
Commercial Real Estate-Other [Member] | Substandard [Member]
Risk Category Of Loans [Line Items]
Total	43,636	38,252
Commercial Real Estate-Other [Member] | Doubtful [Member]
Risk Category Of Loans [Line Items]
Total	$ 58,975	$ 89,764