Covered loans past due status (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held-in-portfolio	$ 24,682,139	$ 24,951,299
Commercial Real Estate Construction Financing Receivable Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held-in-portfolio	719,508	786,765
Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held-in-portfolio	7,016,449	6,691,414
Consumer Portfolio Segment Member
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held-in-portfolio	3,964,445	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	123,860	76,005
Financing Receivable Recorded Investment 60 To 89 Days Past Due	62,090	58,815
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	1,091,800	1,265,530
Total Past Due	1,277,750	1,400,350
Financing Receivable Recorded Investment Current	2,738,580	2,948,353
Loans held-in-portfolio	4,016,330	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	58,948	35,286
Financing Receivable Recorded Investment 60 To 89 Days Past Due	27,865	25,273
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	464,855	519,222
Total Past Due	551,668	579,781
Financing Receivable Recorded Investment Current	1,593,387	1,691,514
Loans held-in-portfolio	2,145,055	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	2,384	4,438
Financing Receivable Recorded Investment 60 To 89 Days Past Due	1,446	1,390
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	71,284	99,555
Total Past Due	75,114	105,383
Financing Receivable Recorded Investment Current	111,007	136,064
Loans held-in-portfolio	186,121	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	24,393	997
Financing Receivable Recorded Investment 60 To 89 Days Past Due	2,391	625
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	359,994	434,661
Total Past Due	386,778	436,283
Financing Receivable Recorded Investment Current	82,987	110,543
Loans held-in-portfolio	469,765	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	32,445	32,371
Financing Receivable Recorded Investment 60 To 89 Days Past Due	27,434	28,238
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	181,393	196,541
Total Past Due	241,272	257,150
Financing Receivable Recorded Investment Current	875,204	915,804
Loans held-in-portfolio	1,116,476	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	5,690	2,913
Financing Receivable Recorded Investment 60 To 89 Days Past Due	2,954	3,289
Financing Receivable Recorded Investment Equal To Greater Than 90 Days Past Due	14,274	15,551
Total Past Due	22,918	21,753
Financing Receivable Recorded Investment Current	75,995	94,428
Loans held-in-portfolio	$ 98,913	$ 116,181