Loans - Schedule of Credit Quality Indicators of Various Classes of Loans (Detail) (Commercial loans [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	$ 8,345,688	$ 8,062,158
Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	4,927,460	3,325,972
Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	3,265,340	4,496,644
Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	152,888	239,542
Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	7,555,133	7,010,406
Pass [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	4,521,932	3,019,100
Pass [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	3,011,320	3,974,463
Pass [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	21,881	16,843
Pass-Watch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	175,127	150,041
Pass-Watch [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	82,605	76,393
Pass-Watch [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	71,405	60,042
Pass-Watch [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	21,117	13,606
Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	131,049	170,375
Special Mention [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	83,985	35,155
Special Mention [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	39,631	125,852
Special Mention [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	7,433	9,368
Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	430,145	653,628
Substandard [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	238,486	194,900
Substandard [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	142,618	334,357
Substandard [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	49,041	124,371
Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	54,234	77,596
Doubtful [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	452	424
Doubtful [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	366	1,930
Doubtful [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade	53,416	75,242
Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade		112
Loss [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial credit risk profile by internally assigned grade		$ 112