Loans - Recorded Investment in Loan Classes Based on Payment Activity (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 4,905,091	$ 4,968,861
PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,115,421	2,240,471
Performing Loans | Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	4,886,537	4,948,725
Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,082,434	2,201,846
Non-Performing Loans | Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	18,554	20,136
Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	32,987	38,625
Commercial and industrial | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	360,603	383,942
Commercial and industrial | Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	351,442	373,665
Commercial and industrial | Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	9,161	10,277
Commercial real estate loans | PCI Loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,280,165	1,355,104
Commercial real estate loans | PCI Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	142,498	147,253
Commercial real estate loans | Performing Loans | PCI Loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,266,695	1,342,030
Commercial real estate loans | Performing Loans | PCI Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	141,319	141,547
Commercial real estate loans | Non-Performing Loans | PCI Loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	13,470	13,074
Commercial real estate loans | Non-Performing Loans | PCI Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,179	5,706
Residential mortgage | Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,892,643	2,912,079
Residential mortgage | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	209,171	218,462
Residential mortgage | Performing Loans | Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,875,896	2,894,149
Residential mortgage | Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	205,928	214,713
Residential mortgage | Non-Performing Loans | Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	16,747	17,930
Residential mortgage | Non-Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,243	3,749
Consumer | Non-PCI Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	380,459	391,809
Consumer | Non-PCI Loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,187,742	1,238,826
Consumer | Non-PCI Loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	444,247	426,147
Consumer | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	122,984	135,710
Consumer | Performing Loans | Non-PCI Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	378,774	389,721
Consumer | Performing Loans | Non-PCI Loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,187,620	1,238,708
Consumer | Performing Loans | Non-PCI Loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	444,247	426,147
Consumer | Performing Loans | PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	117,050	129,891
Consumer | Non-Performing Loans | Non-PCI Loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,685	2,088
Consumer | Non-Performing Loans | Non-PCI Loans | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	122	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	$ 5,934	$ 5,819