Loans - Recorded Investment in Loan Classes Based on Payment Activity (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Non-PCI Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 4,968,861	$ 4,262,349
Non-PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2,912,079	2,419,044
Non-PCI Loans [Member] | Consumer [Member] | Home equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	391,809	400,136
Non-PCI Loans [Member] | Consumer [Member] | Automobile loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,238,826	1,144,780
Non-PCI Loans [Member] | Consumer [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	426,147	298,389
PCI Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2,240,471	1,721,801
PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	218,462	157,328
PCI Loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	135,710	109,110
PCI Loans [Member] | Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	383,942	291,184
PCI Loans [Member] | Commercial real estate [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,355,104	1,107,139
PCI Loans [Member] | Commercial real estate [Member] | Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	147,253	57,040
Performing Loans [Member] | Non-PCI Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,948,725	4,242,380
Performing Loans [Member] | Non-PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2,894,149	2,401,284
Performing Loans [Member] | Non-PCI Loans [Member] | Consumer [Member] | Home equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	389,721	398,114
Performing Loans [Member] | Non-PCI Loans [Member] | Consumer [Member] | Automobile loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,238,708	1,144,690
Performing Loans [Member] | Non-PCI Loans [Member] | Consumer [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	426,147	298,292
Performing Loans [Member] | PCI Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2,201,846	1,674,088
Performing Loans [Member] | PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	214,713	153,789
Performing Loans [Member] | PCI Loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	129,891	103,686
Performing Loans [Member] | PCI Loans [Member] | Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	373,665	272,027
Performing Loans [Member] | PCI Loans [Member] | Commercial real estate [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,342,030	1,091,784
Performing Loans [Member] | PCI Loans [Member] | Commercial real estate [Member] | Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	141,547	52,802
Non-Performing Loans [Member] | Non-PCI Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	20,136	19,969
Non-Performing Loans [Member] | Non-PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	17,930	17,760
Non-Performing Loans [Member] | Non-PCI Loans [Member] | Consumer [Member] | Home equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2,088	2,022
Non-Performing Loans [Member] | Non-PCI Loans [Member] | Consumer [Member] | Automobile loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	118	90
Non-Performing Loans [Member] | Non-PCI Loans [Member] | Consumer [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	0	97
Non-Performing Loans [Member] | PCI Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	38,625	47,713
Non-Performing Loans [Member] | PCI Loans [Member] | Residential mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	3,749	3,539
Non-Performing Loans [Member] | PCI Loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	5,819	5,424
Non-Performing Loans [Member] | PCI Loans [Member] | Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	10,277	19,157
Non-Performing Loans [Member] | PCI Loans [Member] | Commercial real estate [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	13,074	15,355
Non-Performing Loans [Member] | PCI Loans [Member] | Commercial real estate [Member] | Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 5,706	$ 4,238