Loans - Past Due, Non-Accrual and Current Non-Covered Loans by Loan Portfolio Class (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due Loans	$ 43,000	$ 49,686
Accruing Loans 90 Days Or More Past Due	3,100	8,665
Non-Accrual Loans	118,523	131,808
Total Past Due Loans	164,623	190,159
Current Non-PCI Loans	9,766,997	9,664,976
Total Non-PCI Loans	9,931,620	9,855,135
Commercial real estate loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due Loans	24,718	19,930
Accruing Loans 90 Days Or More Past Due	409	5,525
Non-Accrual Loans	69,007	73,430
Total Past Due Loans	94,134	98,885
Current Non-PCI Loans	4,203,442	4,073,054
Total Non-PCI Loans	4,297,576	4,171,939
Consumer loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due Loans	4,138	7,227
Accruing Loans 90 Days Or More Past Due	349	501
Non-Accrual Loans	2,549	3,331
Total Past Due Loans	7,036	11,059
Current Non-PCI Loans	1,428,306	1,393,767
Total Non-PCI Loans	1,435,342	1,404,826
Commercial and industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due Loans	3,525	3,578
Accruing Loans 90 Days Or More Past Due		283
Non-Accrual Loans	20,913	22,424
Total Past Due Loans	24,438	26,285
Current Non-PCI Loans	1,776,380	1,806,458
Total Non-PCI Loans	1,800,818	1,832,743
Commercial real estate [Member] | Commercial real estate loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due Loans	18,946	13,245
Accruing Loans 90 Days Or More Past Due	259	2,950
Non-Accrual Loans	55,390	58,625
Total Past Due Loans	74,595	74,820
Current Non-PCI Loans	3,818,897	3,697,264
Total Non-PCI Loans	3,893,492	3,772,084
Construction [Member] | Commercial real estate loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due Loans	5,772	6,685
Accruing Loans 90 Days Or More Past Due	150	2,575
Non-Accrual Loans	13,617	14,805
Total Past Due Loans	19,539	24,065
Current Non-PCI Loans	384,545	375,790
Total Non-PCI Loans	404,084	399,855
Residential mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due Loans	10,619	18,951
Accruing Loans 90 Days Or More Past Due	2,342	2,356
Non-Accrual Loans	26,054	32,623
Total Past Due Loans	39,015	53,930
Current Non-PCI Loans	2,358,869	2,391,697
Total Non-PCI Loans	2,397,884	2,445,627
Home equity [Member] | Consumer loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due Loans	724	702
Accruing Loans 90 Days Or More Past Due
Non-Accrual Loans	2,328	2,398
Total Past Due Loans	3,052	3,100
Current Non-PCI Loans	412,449	435,781
Total Non-PCI Loans	415,501	438,881
Automobile [Member] | Consumer loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due Loans	3,307	5,443
Accruing Loans 90 Days Or More Past Due	152	469
Non-Accrual Loans	221	305
Total Past Due Loans	3,680	6,217
Current Non-PCI Loans	831,591	780,311
Total Non-PCI Loans	835,271	786,528
Other consumer [Member] | Consumer loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due Loans	107	1,082
Accruing Loans 90 Days Or More Past Due	197	32
Non-Accrual Loans		628
Total Past Due Loans	304	1,742
Current Non-PCI Loans	184,266	177,675
Total Non-PCI Loans	$ 184,570	$ 179,417