Loans and Allowances for Loan Losses - Loans, Net of Unearned Income (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Loans Receivable [Line Items]
Total commercial	$ 4,425,286	$ 4,433,288
Total construction	992,820	989,306
Total real estate	2,873,403	2,923,094
Total residential mortgage loans	1,587,519	1,577,944
Total consumer loans	1,603,734	1,654,170
Total loans	11,482,762	11,577,802
Originated loans [Member]
Loans Receivable [Line Items]
Total commercial	2,900,855	2,713,385
Total construction	697,989	665,673
Total real estate	1,562,383	1,548,402
Total residential mortgage loans	886,232	827,985
Total consumer loans	1,331,477	1,351,776
Total loans	7,378,936	7,107,221
Acquired loans [Member]
Loans Receivable [Line Items]
Total commercial	1,500,137	1,690,643
Total construction	269,727	295,151
Total real estate	1,226,854	1,279,546
Total residential mortgage loans	449,500	486,444
Total consumer loans	180,632	202,974
Total loans	3,626,850	3,954,758
Covered loans [Member]
Loans Receivable [Line Items]
Total commercial	24,294	29,260
Total construction	25,104	28,482
Total real estate	84,166	95,146
Total residential mortgage loans	251,787	263,515
Total consumer loans	91,625	99,420
Total loans	$ 476,976	$ 515,823