Loans and Allowance for Loan Losses - Summary of Composition of Non-Accrual Loans by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 157,127	$ 103,270
Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	130,772	73,255
Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	19,287	25,043
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	7,068	4,972
Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	128,041	83,307
Originated loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	112,165	55,046
Originated loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	11,288	24,406
Originated loans [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	4,588	3,855
Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	22,924	1,117
Acquired loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	12,838
Acquired loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	7,606
Acquired loans [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	2,480	1,117
Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	6,162	18,846
Covered loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	5,769	18,209
Covered loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 393	$ 637