Loans and Allowances for Loan Losses - Summary of Age Analysis of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	$ 48,766	$ 85,960
60-89 days past due	15,351	28,347
Greater than 90 days past due	70,048	85,726
Total past due	134,165	200,033
Current	11,348,597	11,377,769
Total loans	11,482,762	11,577,802
Recorded investment > 90 days and accruing	8,076	13,243
Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	27,756	53,189
60-89 days past due	11,099	21,174
Greater than 90 days past due	53,810	65,836
Total past due	92,665	140,199
Current	8,198,844	8,205,489
Total loans	8,291,509	8,345,688
Recorded investment > 90 days and accruing	6,503	9,616
Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	17,207	21,141
60-89 days past due	2,395	4,593
Greater than 90 days past due	11,015	13,489
Total past due	30,617	39,223
Current	1,556,902	1,538,721
Total loans	1,587,519	1,577,944
Recorded investment > 90 days and accruing	314	1,106
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	3,803	11,630
60-89 days past due	1,857	2,580
Greater than 90 days past due	5,223	6,401
Total past due	10,883	20,611
Current	1,592,851	1,633,559
Total loans	1,603,734	1,654,170
Recorded investment > 90 days and accruing	1,259	2,521
Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	35,025	46,246
60-89 days past due	9,737	21,961
Greater than 90 days past due	51,128	54,686
Total past due	95,890	122,893
Current	7,283,046	6,984,328
Total loans	7,378,936	7,107,221
Recorded investment > 90 days and accruing	6,113	7,736
Originated loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	20,750	24,398
60-89 days past due	7,017	16,508
Greater than 90 days past due	43,808	46,355
Total past due	71,575	87,261
Current	5,089,652	4,840,199
Total loans	5,161,227	4,927,460
Recorded investment > 90 days and accruing	4,854	5,262
Originated loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	10,991	11,500
60-89 days past due	1,234	3,303
Greater than 90 days past due	3,666	4,100
Total past due	15,891	18,903
Current	870,341	809,082
Total loans	886,232	827,985
Originated loans [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	3,284	10,348
60-89 days past due	1,486	2,150
Greater than 90 days past due	3,654	4,231
Total past due	8,424	16,729
Current	1,323,053	1,335,047
Total loans	1,331,477	1,351,776
Recorded investment > 90 days and accruing	1,259	2,474
Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	13,741	39,714
60-89 days past due	5,614	6,386
Greater than 90 days past due	14,699	26,940
Total past due	34,054	73,040
Current	3,592,796	3,881,718
Total loans	3,626,850	3,954,758
Recorded investment > 90 days and accruing	1,963	5,507
Acquired loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	7,006	28,791
60-89 days past due	4,082	4,666
Greater than 90 days past due	6,174	15,774
Total past due	17,262	49,231
Current	2,979,456	3,216,109
Total loans	2,996,718	3,265,340
Recorded investment > 90 days and accruing	1,649	4,354
Acquired loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	6,216	9,641
60-89 days past due	1,161	1,290
Greater than 90 days past due	6,956	8,996
Total past due	14,333	19,927
Current	435,167	466,517
Total loans	449,500	486,444
Recorded investment > 90 days and accruing	314	1,106
Acquired loans [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	519	1,282
60-89 days past due	371	430
Greater than 90 days past due	1,569	2,170
Total past due	2,459	3,882
Current	178,173	199,092
Total loans	180,632	202,974
Recorded investment > 90 days and accruing		47
Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Greater than 90 days past due	4,221	4,100
Total past due	4,221	4,100
Current	472,755	511,723
Total loans	476,976	515,823
Covered loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Greater than 90 days past due	3,828	3,707
Total past due	3,828	3,707
Current	129,736	149,181
Total loans	133,564	152,888
Covered loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Greater than 90 days past due	393	393
Total past due	393	393
Current	251,394	263,122
Total loans	251,787	263,515
Covered loans [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	91,625	99,420
Total loans	$ 91,625	$ 99,420