Loans - Recorded Investment in Loan Classes Based on Payment Activity (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 4,492,696	$ 4,262,349
Non-PCI Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,559,131	2,419,044
Non-PCI Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	391,793	400,136
Non-PCI Loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,198,035	1,144,780
Non-PCI Loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	343,737	298,389
PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,571,472	1,721,801
PCI Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	260,999	291,184
PCI Loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,011,336	1,107,139
PCI Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	52,787	57,040
PCI Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	144,950	157,328
PCI Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	101,400	109,110
Performing Loans | Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	4,473,572	4,242,380
Performing Loans | Non-PCI Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,541,862	2,401,284
Performing Loans | Non-PCI Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	390,009	398,114
Performing Loans | Non-PCI Loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,198,035	1,144,690
Performing Loans | Non-PCI Loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	343,666	298,292
Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,538,671	1,674,088
Performing Loans | PCI Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	249,905	272,027
Performing Loans | PCI Loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	997,614	1,091,784
Performing Loans | PCI Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	51,875	52,802
Performing Loans | PCI Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	142,068	153,789
Performing Loans | PCI Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	97,209	103,686
Non-Performing Loans | Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	19,124	19,969
Non-Performing Loans | Non-PCI Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	17,269	17,760
Non-Performing Loans | Non-PCI Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,784	2,022
Non-Performing Loans | Non-PCI Loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	0	90
Non-Performing Loans | Non-PCI Loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	71	97
Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	32,801	47,713
Non-Performing Loans | PCI Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	11,094	19,157
Non-Performing Loans | PCI Loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	13,722	15,355
Non-Performing Loans | PCI Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	912	4,238
Non-Performing Loans | PCI Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,882	3,539
Non-Performing Loans | PCI Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 4,191	$ 5,424