Recorded Investment in PCI Loans by Class Based on Individual Loan Payment Activity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 11,148,938	$ 9,799,641
Residential Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,482,363	2,285,590
PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,274,353	271,844
PCI Loans | Commercial and Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	322,926	83,742
PCI Loans | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	828,679	160,651
PCI Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	43,398	6,974
PCI Loans | Residential Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	28,951	15,546
PCI Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	50,399	4,931
Performing Financing Receivable | Residential Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,450,799	2,253,944
Performing Financing Receivable | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,195,703	195,143
Performing Financing Receivable | PCI Loans | Commercial and Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	318,415	67,424
Performing Financing Receivable | PCI Loans | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	770,914	112,047
Performing Financing Receivable | PCI Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	32,927	623
Performing Financing Receivable | PCI Loans | Residential Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	24,473	10,118
Performing Financing Receivable | PCI Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	48,974	4,931
Nonperforming Financing Receivable | Residential Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	31,564	31,646
Nonperforming Financing Receivable | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	78,650	76,701
Nonperforming Financing Receivable | PCI Loans | Commercial and Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	4,511	16,318
Nonperforming Financing Receivable | PCI Loans | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	57,765	48,604
Nonperforming Financing Receivable | PCI Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	10,471	6,351
Nonperforming Financing Receivable | PCI Loans | Residential Mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	4,478	5,428
Nonperforming Financing Receivable | PCI Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 1,425