Loans and Leases (Allowance For Loan And Lease Losses By Portfolio Segment) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016		Dec. 31, 2015		Jun. 30, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	$ 174,201	$ 161,970	$ 174,990	$ 159,264
Provision (benefit) charged to expense	14,000	12,750	29,600	22,500
Charge-offs	(9,784)	(8,961)	(28,684)	(18,635)
Recoveries	2,011	2,101	4,522	4,731
Balance, end of period	174,201	161,970	174,990	159,264	$ 180,428		$ 174,990		$ 167,860
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment					21,133				30,689
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment					159,295				137,171
Financing Receivable, Individually Evaluated for Impairment					267,720				301,923
Financing Receivable, Collectively Evaluated for Impairment					16,004,309				14,475,603
Loans and leases					16,272,029	[1],[2]	15,671,735	[1],[2]	14,777,526
Residential Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	27,330	27,749	25,876	25,452
Provision (benefit) charged to expense	(2,412)	(2,194)	(85)	1,950
Charge-offs	(638)	(1,461)	(2,232)	(3,416)
Recoveries	133	369	854	477
Balance, end of period	27,330	27,749	25,876	25,452	24,413		25,876		24,463
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment					10,018				10,592
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment					14,395				13,871
Financing Receivable, Individually Evaluated for Impairment					127,965				138,810
Financing Receivable, Collectively Evaluated for Impairment					4,028,700				3,694,680
Loans and leases					4,156,665		4,061,001		3,833,490
Consumer Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	41,636	42,616	42,052	43,518
Provision (benefit) charged to expense	4,682	995	7,473	3,227
Charge-offs	(4,556)	(3,853)	(8,977)	(8,149)
Recoveries	1,194	1,049	2,408	2,211
Balance, end of period	41,636	42,616	42,052	43,518	42,956		42,052		40,807
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment					3,027				3,564
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment					39,929				37,243
Financing Receivable, Individually Evaluated for Impairment					47,576				49,119
Financing Receivable, Collectively Evaluated for Impairment					2,680,876				2,557,320
Loans and leases					2,728,452		2,702,560		2,606,439
Commercial Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	66,471	55,628	66,686	52,114
Provision (benefit) charged to expense	10,560	12,625	21,096	15,379
Charge-offs	(3,525)	(2,541)	(14,733)	(2,796)
Recoveries	316	529	773	1,544
Balance, end of period	66,471	55,628	66,686	52,114	73,822		66,686		66,241
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment					6,422				11,703
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment					67,400				54,538
Financing Receivable, Individually Evaluated for Impairment					59,550				54,811
Financing Receivable, Collectively Evaluated for Impairment					4,517,932				3,967,094
Loans and leases					4,577,482		4,315,999		4,021,905
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	33,318	30,549	34,889	32,102
Provision (benefit) charged to expense	1,087	1,258	968	2,656
Charge-offs	(995)	(1,091)	(2,521)	(4,244)
Recoveries	212	52	286	254
Balance, end of period	33,318	30,549	34,889	32,102	33,622		34,889		30,768
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment					1,649				4,824
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment					31,973				25,944
Financing Receivable, Individually Evaluated for Impairment					32,208				59,063
Financing Receivable, Collectively Evaluated for Impairment					4,158,879				3,711,189
Loans and leases					4,191,087		3,991,649		3,770,252
Finance Leases Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	5,446	5,428	5,487	6,078
Provision (benefit) charged to expense	83	66	148	(712)
Charge-offs	(70)	(15)	(221)	(30)
Recoveries	156	102	201	245
Balance, end of period	$ 5,446	$ 5,428	$ 5,487	$ 6,078	5,615		5,487		5,581
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment					17				6
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment					5,598				5,575
Financing Receivable, Individually Evaluated for Impairment					421				120
Financing Receivable, Collectively Evaluated for Impairment					617,922				545,320
Loans and leases					$ 618,343		$ 600,526		$ 545,440

[1] At June 30, 2016, the Company had pledged $6.1 billion of eligible residential and consumer loans as collateral to support borrowing capacity at the FHLB Boston and the FRB of Boston.

[2] Loans and leases include net deferred fees and net premiums and discounts of $20.0 million and $18.0 million at June 30, 2016 and December 31, 2015, respectively.