Loans - Recorded Investment in Loan Classes Based on Payment Activity (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Non-PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 4,768,989	$ 4,968,861
Non-PCI Loans | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2,684,195	2,912,079
Non-PCI Loans | Consumer | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total Loans	376,213	391,809
Non-PCI Loans | Consumer | Automobile
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,139,082	1,238,826
Non-PCI Loans | Consumer | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Total Loans	569,499	426,147
Non-PCI Loans | Performing Loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,755,740	4,948,725
Non-PCI Loans | Performing Loans | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2,672,120	2,894,149
Non-PCI Loans | Performing Loans | Consumer | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total Loans	375,185	389,721
Non-PCI Loans | Performing Loans | Consumer | Automobile
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,138,936	1,238,708
Non-PCI Loans | Performing Loans | Consumer | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Total Loans	569,499	426,147
Non-PCI Loans | Non-Performing Loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans	13,249	20,136
Non-PCI Loans | Non-Performing Loans | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total Loans	12,075	17,930
Non-PCI Loans | Non-Performing Loans | Consumer | Home equity
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,028	2,088
Non-PCI Loans | Non-Performing Loans | Consumer | Automobile
Financing Receivable, Recorded Investment [Line Items]
Total Loans	146	118
Non-PCI Loans | Non-Performing Loans | Consumer | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	0
PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,771,502	2,240,471
PCI Loans | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total Loans	183,723	218,462
PCI Loans | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total Loans	100,583	135,710
PCI Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total Loans	281,177	383,942
PCI Loans | Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,091,339	1,355,104
PCI Loans | Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Total Loans	114,680	147,253
PCI Loans | Performing Loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,744,491	2,201,846
PCI Loans | Performing Loans | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total Loans	179,793	214,713
PCI Loans | Performing Loans | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total Loans	98,469	129,891
PCI Loans | Performing Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total Loans	272,483	373,665
PCI Loans | Performing Loans | Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,080,376	1,342,030
PCI Loans | Performing Loans | Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Total Loans	113,370	141,547
PCI Loans | Non-Performing Loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans	27,011	38,625
PCI Loans | Non-Performing Loans | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Total Loans	3,930	3,749
PCI Loans | Non-Performing Loans | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2,114	5,819
PCI Loans | Non-Performing Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total Loans	8,694	10,277
PCI Loans | Non-Performing Loans | Commercial real estate | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans	10,963	13,074
PCI Loans | Non-Performing Loans | Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,310	$ 5,706