Loans and Allowance for Loan Losses - Summary of Age Analysis of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	$ 48,626	$ 45,381
60-89 past due	21,829	8,218
Greater than 90 days past due	101,613	109,150
Total past due	172,068	162,749
Current	11,262,380	11,014,277
Total Loans	11,434,448	11,177,026
Recorded investment > 90 days and accruing	8,906	5,880
Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	26,658	43,683
60-89 past due	12,964	7,788
Greater than 90 days past due	79,120	88,178
Total past due	118,742	139,649
Current	6,462,452	4,748,081
Total Loans	6,581,194	4,887,730
Recorded investment > 90 days and accruing	6,423	4,871
Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	21,968	1,698
60-89 past due	8,865	430
Greater than 90 days past due	17,072	2,126
Total past due	47,905	4,254
Current	4,249,617	5,613,599
Total Loans	4,297,522	5,617,853
Recorded investment > 90 days and accruing	2,483	1,009
Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Greater than 90 days past due	5,421	18,846
Total past due	5,421	18,846
Current	550,311	652,597
Total Loans	555,732	671,443
Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	39,615	23,996
60-89 past due	15,682	943
Greater than 90 days past due	78,708	77,076
Total past due	134,005	102,015
Current	8,053,464	7,960,143
Total Loans	8,187,469	8,062,158
Recorded investment > 90 days and accruing	5,454	3,821
Commercial loans [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	21,202	23,996
60-89 past due	9,456	943
Greater than 90 days past due	64,986	58,867
Total past due	95,644	83,806
Current	4,370,092	3,242,166
Total Loans	4,465,736	3,325,972
Recorded investment > 90 days and accruing	4,019	3,821
Commercial loans [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	18,413
60-89 past due	6,226
Greater than 90 days past due	8,694
Total past due	33,333
Current	3,511,676	4,496,644
Total Loans	3,545,009	4,496,644
Recorded investment > 90 days and accruing	1,435
Commercial loans [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Greater than 90 days past due	5,028	18,209
Total past due	5,028	18,209
Current	171,696	221,333
Total Loans	176,724	239,542
Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	3,048	17,884
60-89 past due	4,521	4,364
Greater than 90 days past due	15,952	26,037
Total past due	23,521	48,285
Current	1,538,119	1,459,213
Total Loans	1,561,640	1,507,498
Recorded investment > 90 days and accruing	1,020	994
Residential mortgage loans [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	118	17,884
60-89 past due	2,175	4,364
Greater than 90 days past due	9,120	25,400
Total past due	11,413	47,648
Current	746,058	439,499
Total Loans	757,471	487,147
Recorded investment > 90 days and accruing		994
Residential mortgage loans [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	2,930
60-89 past due	2,346
Greater than 90 days past due	6,439
Total past due	11,715
Current	520,836	734,669
Total Loans	532,551	734,669
Recorded investment > 90 days and accruing	1,020
Residential mortgage loans [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Greater than 90 days past due	393	637
Total past due	393	637
Current	271,225	285,045
Total Loans	271,618	285,682
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	5,963	3,501
60-89 past due	1,626	2,911
Greater than 90 days past due	6,953	6,037
Total past due	14,542	12,449
Current	1,670,797	1,594,921
Total Loans	1,685,339	1,607,370
Recorded investment > 90 days and accruing	2,432	1,065
Consumer loans [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	5,338	1,803
60-89 past due	1,333	2,481
Greater than 90 days past due	5,014	3,911
Total past due	11,685	8,195
Current	1,346,302	1,066,416
Total Loans	1,357,987	1,074,611
Recorded investment > 90 days and accruing	2,404	56
Consumer loans [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	625	1,698
60-89 past due	293	430
Greater than 90 days past due	1,939	2,126
Total past due	2,857	4,254
Current	217,105	382,286
Total Loans	219,962	386,540
Recorded investment > 90 days and accruing	28	1,009
Consumer loans [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	107,390	146,219
Total Loans	$ 107,390	$ 146,219