Loans and Allowances for Loan Losses - Summary of Composition of Non-Accrual Loans by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	$ 136,350	$ 137,615
Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	108,480	112,517
Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	21,218	18,649
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	6,652	6,449
Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	98,047	103,428
Originated loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	84,049	91,908
Originated loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	9,522	7,705
Originated loans [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	4,476	3,815
Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	34,082	30,087
Acquired loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	20,603	16,902
Acquired loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	11,303	10,551
Acquired loans [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	2,176	2,634
Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	4,221	4,100
Covered loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	3,828	3,707
Covered loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Accrual Loans	$ 393	$ 393