Loans - Recorded Investment in Loan Classes Based on Payment Activity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Non-PCI Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 3,850,453	$ 3,664,318
Non-PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,445,627	2,285,590
Non-PCI Loans [Member] | Home equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	438,881	469,604
Non-PCI Loans [Member] | Automobile loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	786,528	772,490
Non-PCI Loans [Member] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	179,417	136,634
PCI Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,167,664	271,844
PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	26,461	15,546
PCI Loans [Member] | Commercial and industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	298,600	83,742
PCI Loans [Member] | Commercial real estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	765,893	160,651
PCI Loans [Member] | Construction [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	27,513	6,974
PCI Loans [Member] | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	49,197	4,931
Performing Loans [Member] | Non-PCI Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,814,499	3,628,762
Performing Loans [Member] | Non-PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,413,004	2,253,944
Performing Loans [Member] | Non-PCI Loans [Member] | Home equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	436,483	466,904
Performing Loans [Member] | Non-PCI Loans [Member] | Automobile loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	786,223	772,029
Performing Loans [Member] | Non-PCI Loans [Member] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	178,789	135,885
Performing Loans [Member] | PCI Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,095,804	195,143
Performing Loans [Member] | PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	22,173	10,118
Performing Loans [Member] | PCI Loans [Member] | Commercial and industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	292,163	67,424
Performing Loans [Member] | PCI Loans [Member] | Commercial real estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	715,812	112,047
Performing Loans [Member] | PCI Loans [Member] | Construction [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	17,967	623
Performing Loans [Member] | PCI Loans [Member] | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	47,689	4,931
Non-Performing Loans [Member] | Non-PCI Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	35,954	35,556
Non-Performing Loans [Member] | Non-PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	32,623	31,646
Non-Performing Loans [Member] | Non-PCI Loans [Member] | Home equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,398	2,700
Non-Performing Loans [Member] | Non-PCI Loans [Member] | Automobile loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	305	461
Non-Performing Loans [Member] | Non-PCI Loans [Member] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	628	749
Non-Performing Loans [Member] | PCI Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	71,860	76,701
Non-Performing Loans [Member] | PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	4,288	5,428
Non-Performing Loans [Member] | PCI Loans [Member] | Commercial and industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	6,437	16,318
Non-Performing Loans [Member] | PCI Loans [Member] | Commercial real estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	50,081	48,604
Non-Performing Loans [Member] | PCI Loans [Member] | Construction [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	9,546	6,351
Non-Performing Loans [Member] | PCI Loans [Member] | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 1,508