Allowance for Loan Losses and Credit Quality Information - Schedule of Commercial Credit Exposure Credit Risk Profile by Internally Assigned Risk Rating (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	100.00%	100.00%
Accrual	$ 2,321,342	$ 2,239,812
Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	34,851	73,729
Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	115,287	119,950
Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	12,760	22,019
Doubtful/Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	17,382	11,024
Total Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	8.00%	10.00%
Accrual	180,280	226,722
Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	92.00%	90.00%
Accrual	2,141,062	2,013,090
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	739,629	704,491
Commercial [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	19,413	14,611
Commercial [Member] | Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	63,699	63,074
Commercial [Member] | Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	1,984	1,598
Commercial [Member] | Doubtful/Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	4,040	3,263
Commercial [Member] | Total Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	89,136	82,546
Commercial [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	650,493	621,945
Owner-Occupied Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	767,942	770,581
Owner-Occupied Commercial [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	15,134	27,398
Owner-Occupied Commercial [Member] | Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	43,465	44,899
Owner-Occupied Commercial [Member] | Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	5,390	13,827
Owner-Occupied Commercial [Member] | Doubtful/Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	7,291	174
Owner-Occupied Commercial [Member] | Total Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	71,280	86,298
Owner-Occupied Commercial [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	696,662	684,283
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	688,233	631,365
Commercial Mortgages [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	304	29,267
Commercial Mortgages [Member] | Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	5,111	6,222
Commercial Mortgages [Member] | Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	4,740	5,422
Commercial Mortgages [Member] | Doubtful/Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	6,051	7,212
Commercial Mortgages [Member] | Total Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	16,206	48,123
Commercial Mortgages [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	672,027	583,242
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	125,538	133,375
Construction [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual		2,453
Construction [Member] | Accrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	3,012	5,755
Construction [Member] | Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	646	1,172
Construction [Member] | Doubtful/Nonaccrual [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual		375
Construction [Member] | Total Special Mention, Substandard and Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	3,658	9,755
Construction [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual	$ 121,880	$ 123,620