Covered loans past due status (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held-in-portfolio	$ 24,657,720	$ 24,951,299
Commercial Real Estate Construction Financing Receivable Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held-in-portfolio	651,554	786,765
Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held-in-portfolio	7,129,273	6,691,414
Consumer Portfolio Segment Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held-in-portfolio	3,920,038	3,789,936
Covered Under Loss Sharing Agreements With F D I C [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	56,774	76,005
Financing Receivable Recorded Investment 60 To 89 Days Past Due	135,775	58,815
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	1,075,358	1,265,530
Total Past Due	1,267,907	1,400,350
Financing Receivable Recorded Investment Current	2,635,960	2,948,353
Loans held-in-portfolio	3,903,867	4,348,703
Covered Under Loss Sharing Agreements With F D I C [Member] | Commercial Real Estate Portfolio Segment Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	24,365	35,286
Financing Receivable Recorded Investment 60 To 89 Days Past Due	114,519	25,273
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	491,418	519,222
Total Past Due	630,302	579,781
Financing Receivable Recorded Investment Current	1,523,488	1,691,514
Loans held-in-portfolio	2,153,790	2,271,295
Covered Under Loss Sharing Agreements With F D I C [Member] | Commercial And Industrial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	2,736	4,438
Financing Receivable Recorded Investment 60 To 89 Days Past Due	1,728	1,390
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	63,356	99,555
Total Past Due	67,820	105,383
Financing Receivable Recorded Investment Current	102,752	136,064
Loans held-in-portfolio	170,572	241,447
Covered Under Loss Sharing Agreements With F D I C [Member] | Commercial Real Estate Construction Financing Receivable Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	809	997
Financing Receivable Recorded Investment 60 To 89 Days Past Due	0	625
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	318,051	434,661
Total Past Due	318,860	436,283
Financing Receivable Recorded Investment Current	74,241	110,543
Loans held-in-portfolio	393,101	546,826
Covered Under Loss Sharing Agreements With F D I C [Member] | Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	27,195	32,371
Financing Receivable Recorded Investment 60 To 89 Days Past Due	17,506	28,238
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	191,011	196,541
Total Past Due	235,712	257,150
Financing Receivable Recorded Investment Current	871,139	915,804
Loans held-in-portfolio	1,106,851	1,172,954
Covered Under Loss Sharing Agreements With F D I C [Member] | Consumer Portfolio Segment Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due	1,669	2,913
Financing Receivable Recorded Investment 60 To 89 Days Past Due	2,022	3,289
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	11,522	15,551
Total Past Due	15,213	21,753
Financing Receivable Recorded Investment Current	64,340	94,428
Loans held-in-portfolio	$ 79,553	$ 116,181