Loans - Recorded Investment in Loan Classes Based on Payment Activity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Non-PCI Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 3,758,143	$ 3,850,453
Non-PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,336,821	2,445,627
Non-PCI Loans [Member] | Home equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	421,698	438,881
Non-PCI Loans [Member] | Automobile loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	811,060	786,528
Non-PCI Loans [Member] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	188,564	179,417
PCI Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,071,028	1,167,664
PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	24,750	26,461
PCI Loans [Member] | Commercial and industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	268,644	298,600
PCI Loans [Member] | Commercial real estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	703,196	765,893
PCI Loans [Member] | Construction [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	31,621	27,513
PCI Loans [Member] | Consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	42,817	49,197
Performing Loans [Member] | Non-PCI Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,723,472	3,814,499
Performing Loans [Member] | Non-PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,304,916	2,413,004
Performing Loans [Member] | Non-PCI Loans [Member] | Home equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	419,750	436,483
Performing Loans [Member] | Non-PCI Loans [Member] | Automobile loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	810,809	786,223
Performing Loans [Member] | Non-PCI Loans [Member] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	187,997	178,789
Performing Loans [Member] | PCI Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,001,906	1,095,804
Performing Loans [Member] | PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	21,059	22,173
Performing Loans [Member] | PCI Loans [Member] | Commercial and industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	264,578	292,163
Performing Loans [Member] | PCI Loans [Member] | Commercial real estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	654,900	715,812
Performing Loans [Member] | PCI Loans [Member] | Construction [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	19,861	17,967
Performing Loans [Member] | PCI Loans [Member] | Consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	41,508	47,689
Non-Performing Loans [Member] | Non-PCI Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	34,671	35,954
Non-Performing Loans [Member] | Non-PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	31,905	32,623
Non-Performing Loans [Member] | Non-PCI Loans [Member] | Home equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,948	2,398
Non-Performing Loans [Member] | Non-PCI Loans [Member] | Automobile loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	251	305
Non-Performing Loans [Member] | Non-PCI Loans [Member] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	567	628
Non-Performing Loans [Member] | PCI Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	69,122	71,860
Non-Performing Loans [Member] | PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,691	4,288
Non-Performing Loans [Member] | PCI Loans [Member] | Commercial and industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	4,066	6,437
Non-Performing Loans [Member] | PCI Loans [Member] | Commercial real estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	48,296	50,081
Non-Performing Loans [Member] | PCI Loans [Member] | Construction [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	11,760	9,546
Non-Performing Loans [Member] | PCI Loans [Member] | Consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 1,309	$ 1,508