Loans and Allowance for Loan Losses - Loans, Net of Unearned Income (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total commercial	$ 4,235,825	$ 3,800,230
Total construction	1,044,637	1,263,005
Total real estate	2,907,007	2,998,923
Total residential mortgage loans	1,561,640	1,507,498
Total consumer loans	1,685,339	1,607,370
Total Loans	11,434,448	11,177,026
Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total commercial	2,416,143	1,525,409
Total construction	628,067	540,806
Total real estate	1,421,526	1,259,757
Total residential mortgage loans	757,471	487,147
Total consumer loans	1,357,987	1,074,611
Total Loans	6,581,194	4,887,730
Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total commercial	1,797,827	2,236,758
Total construction	368,476	603,371
Total real estate	1,378,706	1,656,515
Total residential mortgage loans	532,551	734,669
Total consumer loans	219,962	386,540
Total Loans	4,297,522	5,617,853
Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total commercial	21,855	38,063
Total construction	48,094	118,828
Total real estate	106,775	82,651
Total residential mortgage loans	271,618	285,682
Total consumer loans	107,390	146,219
Total Loans	$ 555,732	$ 671,443