Loans - Recorded Investment Based on Payment Activity (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 5,006,437	$ 4,768,989
Non-PCI Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,791,779	2,684,195
Non-PCI Loans | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	371,130	376,213
Non-PCI Loans | Consumer | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,171,579	1,139,082
Non-PCI Loans | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	671,949	569,499
Non-PCI Loans | Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	4,991,619	4,755,740
Non-PCI Loans | Performing Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,778,805	2,672,120
Non-PCI Loans | Performing Loans | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	369,364	375,185
Non-PCI Loans | Performing Loans | Consumer | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,171,501	1,138,936
Non-PCI Loans | Performing Loans | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	671,949	569,499
Non-PCI Loans | Non-Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	14,818	13,249
Non-PCI Loans | Non-Performing Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	12,974	12,075
Non-PCI Loans | Non-Performing Loans | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,766	1,028
Non-PCI Loans | Non-Performing Loans | Consumer | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	78	146
Non-PCI Loans | Non-Performing Loans | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	0	0
PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,471,855	1,771,502
PCI Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	149,656	183,723
PCI Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	83,749	100,583
PCI Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	202,257	281,177
PCI Loans | Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	991,235	1,091,339
PCI Loans | Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	44,958	114,680
PCI Loans | Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,446,442	1,744,491
PCI Loans | Performing Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	144,998	179,793
PCI Loans | Performing Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	83,203	98,469
PCI Loans | Performing Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	189,158	272,483
PCI Loans | Performing Loans | Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	984,789	1,080,376
PCI Loans | Performing Loans | Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	44,294	113,370
PCI Loans | Non-Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	25,413	27,011
PCI Loans | Non-Performing Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	4,658	3,930
PCI Loans | Non-Performing Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	546	2,114
PCI Loans | Non-Performing Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	13,099	8,694
PCI Loans | Non-Performing Loans | Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	6,446	10,963
PCI Loans | Non-Performing Loans | Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 664	$ 1,310