Carrying Value of Loans and Leases by Portfolio Segment Based on Credit Quality Indicators used to Allocate Allowance for Loan and Lease Losses (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	$ 1,500,015	$ 1,398,456
Pass
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	945,454	833,141
Special Mention
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	6,036	9,788
Substandard
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	13,595	21,957
Pass, Special Mention and Substandard
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	965,085	864,886
Performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	529,483	526,981
Non-performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	5,447	6,589
Performing and Non-performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	534,930	533,570
Commercial mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	622,771	546,358
Commercial mortgage | Pass
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	615,742	538,470
Commercial mortgage | Special Mention
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	3,771	2,215
Commercial mortgage | Substandard
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	3,258	5,673
Commercial mortgage | Pass, Special Mention and Substandard
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	622,771	546,358
Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	39,055	26,908
Construction | Pass
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	35,518	16,504
Construction | Special Mention
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses		1,317
Construction | Substandard
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	3,537	9,087
Construction | Pass, Special Mention and Substandard
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	39,055	26,908
Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	303,259	291,620
Commercial and industrial | Pass
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	294,194	278,167
Commercial and industrial | Special Mention
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	2,265	6,256
Commercial and industrial | Substandard
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	6,800	7,197
Commercial and industrial | Pass, Special Mention and Substandard
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	303,259	291,620
Residential mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	291,645	288,212
Residential mortgage | Performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	287,807	284,464
Residential mortgage | Non-performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	3,838	3,748
Residential mortgage | Performing and Non-performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	291,645	288,212
Home equity lines and loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	187,634	194,861
Home equity lines and loans | Performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	186,090	192,069
Home equity lines and loans | Non-performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	1,544	2,792
Home equity lines and loans | Performing and Non-performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	187,634	194,861
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	17,572	17,666
Consumer | Performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	17,523	17,659
Consumer | Non-performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	49	7
Consumer | Performing and Non-performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	17,572	17,666
Leases
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	38,079	32,831
Leases | Performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	38,063	32,789
Leases | Non-performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	16	42
Leases | Performing and Non-performing
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan and lease losses	$ 38,079	$ 32,831