Loans - Recorded Investment in Loan Classes Based on Payment Activity (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 4,868,100	$ 4,968,861
PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,975,401	2,240,471
Performing Loans | Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	4,852,104	4,948,725
Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,944,126	2,201,846
Non-Performing Loans | Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	15,996	20,136
Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	31,275	38,625
Commercial and industrial | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	327,911	383,942
Commercial and industrial | Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	318,935	373,665
Commercial and industrial | Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	8,976	10,277
Commercial real estate loans | PCI Loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,196,144	1,355,104
Commercial real estate loans | PCI Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	136,515	147,253
Commercial real estate loans | Performing Loans | PCI Loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,185,024	1,342,030
Commercial real estate loans | Performing Loans | PCI Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	135,090	141,547
Commercial real estate loans | Non-Performing Loans | PCI Loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	11,120	13,074
Commercial real estate loans | Non-Performing Loans | PCI Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,425	5,706
Residential mortgage | Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,857,190	2,912,079
Residential mortgage | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	198,163	218,462
Residential mortgage | Performing Loans | Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,842,324	2,894,149
Residential mortgage | Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	194,532	214,713
Residential mortgage | Non-Performing Loans | Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	14,866	17,930
Residential mortgage | Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,631	3,749
Consumer | Non-PCI Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	380,200	391,809
Consumer | Non-PCI Loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,141,651	1,238,826
Consumer | Non-PCI Loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	489,059	426,147
Consumer | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	116,668	135,710
Consumer | Performing Loans | Non-PCI Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	379,211	389,721
Consumer | Performing Loans | Non-PCI Loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,141,510	1,238,708
Consumer | Performing Loans | Non-PCI Loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	489,059	426,147
Consumer | Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	110,545	129,891
Consumer | Non-Performing Loans | Non-PCI Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	989	2,088
Consumer | Non-Performing Loans | Non-PCI Loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	141	118
Consumer | Non-Performing Loans | Non-PCI Loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	0	0
Consumer | Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 6,123	$ 5,819