Risk Category of Loans (Excluding PCI Loans) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 1,847,650	$ 1,878,387
Commercial and Industrial | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,672,602	1,669,943
Commercial and Industrial | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	64,492	95,726
Commercial and Industrial | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	110,332	112,186
Commercial and Industrial | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	224	532
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,752,963	3,574,089
Commercial Real Estate | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,549,638	3,350,475
Commercial Real Estate | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	49,531	82,612
Commercial Real Estate | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	153,794	141,002
Commercial Real Estate | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	397,292	411,003
Construction | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	336,396	329,848
Construction | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	34,928	42,845
Construction | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	25,968	38,114
Construction | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		196
Total
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,997,905	5,863,479
Total | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,558,636	5,350,266
Total | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	148,951	221,183
Total | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	290,094	291,302
Total | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 224	$ 728