Loans and Leases (Allowance For Loan And Lease Losses By Portfolio Segment) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017		Dec. 31, 2016		Jun. 30, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	$ 199,107	$ 174,201	$ 194,320	$ 174,990
Provision (benefit) charged to expense	7,250	14,000	17,750	29,600
Charge-offs	(8,640)	(9,784)	(16,256)	(28,684)
Recoveries	1,861	2,011	3,764	4,522
Balance, end of period	199,107	174,201	194,320	174,990	$ 199,578		$ 194,320		$ 180,428
ALLL, Individually evaluated for impairment					18,236				21,133
ALLL, Collectively evaluated for impairment					181,342				159,295
Loan and lease balances, Individually evaluated for impairment					273,345				267,720
Loan and lease balances, Collectively evaluated for impairment					17,000,333				16,004,309
Loans and leases					17,273,678	[1],[2]	17,026,588	[1],[2]	16,272,029
Residential Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	20,264	27,330	23,226	25,876
Provision (benefit) charged to expense	(1,621)	(2,412)	(4,088)	(85)
Charge-offs	(623)	(638)	(1,355)	(2,232)
Recoveries	407	133	644	854
Balance, end of period	20,264	27,330	23,226	25,876	18,427		23,226		24,413
ALLL, Individually evaluated for impairment					5,105				10,018
ALLL, Collectively evaluated for impairment					13,322				14,395
Loan and lease balances, Individually evaluated for impairment					117,820				127,965
Loan and lease balances, Collectively evaluated for impairment					4,270,488				4,028,700
Loans and leases					4,388,308		4,254,682		4,156,665
Consumer Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	45,408	41,636	45,233	42,052
Provision (benefit) charged to expense	1,562	4,682	6,888	7,473
Charge-offs	(5,602)	(4,556)	(12,076)	(8,977)
Recoveries	1,120	1,194	2,443	2,408
Balance, end of period	45,408	41,636	45,233	42,052	42,488		45,233		42,956
ALLL, Individually evaluated for impairment					1,829				3,027
ALLL, Collectively evaluated for impairment					40,659				39,929
Loan and lease balances, Individually evaluated for impairment					47,310				47,576
Loan and lease balances, Collectively evaluated for impairment					2,552,008				2,680,876
Loans and leases					2,599,318		2,684,500		2,728,452
Commercial Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	76,354	66,471	71,905	66,686
Provision (benefit) charged to expense	5,489	10,560	9,739	21,096
Charge-offs	(2,196)	(3,525)	(2,319)	(14,733)
Recoveries	317	316	639	773
Balance, end of period	76,354	66,471	71,905	66,686	79,964		71,905		73,822
ALLL, Individually evaluated for impairment					10,951				6,422
ALLL, Collectively evaluated for impairment					69,013				67,400
Loan and lease balances, Individually evaluated for impairment					83,206				59,550
Loan and lease balances, Collectively evaluated for impairment					5,060,965				4,517,932
Loans and leases					5,144,171		4,940,931		4,577,482
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	50,727	33,318	47,477	34,889
Provision (benefit) charged to expense	1,771	1,087	5,116	968
Charge-offs	(100)	(995)	(202)	(2,521)
Recoveries	4	212	11	286
Balance, end of period	50,727	33,318	47,477	34,889	52,402		47,477		33,622
ALLL, Individually evaluated for impairment					324				1,649
ALLL, Collectively evaluated for impairment					52,078				31,973
Loan and lease balances, Individually evaluated for impairment					18,677				32,208
Loan and lease balances, Collectively evaluated for impairment					4,537,531				4,158,879
Loans and leases					4,556,208		4,510,846		4,191,087
Finance Leases Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning of period	6,354	5,446	6,479	5,487
Provision (benefit) charged to expense	49	83	95	148
Charge-offs	(119)	(70)	(304)	(221)
Recoveries	13	156	27	201
Balance, end of period	$ 6,354	$ 5,446	$ 6,479	$ 5,487	6,297		6,479		5,615
ALLL, Individually evaluated for impairment					27				17
ALLL, Collectively evaluated for impairment					6,270				5,598
Loan and lease balances, Individually evaluated for impairment					6,332				421
Loan and lease balances, Collectively evaluated for impairment					579,341				617,922
Loans and leases					$ 585,673		$ 635,629		$ 618,343

[1] At June 30, 2017, the Company had pledged $6.2 billion of eligible residential, consumer and commercial 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/discounts of $18.8 million and $17.3 million at June 30, 2017 and December 31, 2016, respectively.