Loans and Leases (Summary Of Loan And Lease Portfolio Aging By Class Of Loan) (Detail) - USD ($) $ in Thousands	Jun. 30, 2017		Dec. 31, 2016		Jun. 30, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 195,492		$ 175,864
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	1,185		749
Financing Receivable, Recorded Investment, Nonaccrual Status	166,244		133,816
Financing Receivable, Recorded Investment, Current	17,078,186		16,850,724
Loans and leases	17,273,678	[1],[2]	17,026,588	[1],[2]	$ 16,272,029
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	18,890		28,337
Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	9,173		12,962
Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	55,944		58,519
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0		0
Financing Receivable, Recorded Investment, Nonaccrual Status	46,090		47,279
Financing Receivable, Recorded Investment, Current	4,332,364		4,196,163
Loans and leases	4,388,308		4,254,682		4,156,665
Residential Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	6,157		8,631
Residential Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	3,697		2,609
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases	2,599,318		2,684,500		2,728,452
Consumer Portfolio Segment [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	50,242		50,539
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0		0
Financing Receivable, Recorded Investment, Nonaccrual Status	38,974		35,926
Financing Receivable, Recorded Investment, Current	2,293,538		2,359,354
Loans and leases	2,343,780		2,409,893
Consumer Portfolio Segment [Member] | Home Equity Loan [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	7,961		8,831
Consumer Portfolio Segment [Member] | Home Equity Loan [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	3,307		5,782
Consumer Portfolio Segment [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	4,397		5,381
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0		0
Financing Receivable, Recorded Investment, Nonaccrual Status	1,272		1,663
Financing Receivable, Recorded Investment, Current	251,141		269,226
Loans and leases	255,538		274,607
Consumer Portfolio Segment [Member] | Consumer Borrower [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,788		2,233
Consumer Portfolio Segment [Member] | Consumer Borrower [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,337		1,485
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases	5,144,171		4,940,931		4,577,482
Commercial Portfolio Segment [Member] | Commercial and Industrial Sector [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	71,283		40,898
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	1,185		749
Financing Receivable, Recorded Investment, Nonaccrual Status	68,181		38,190
Financing Receivable, Recorded Investment, Current	4,211,685		4,094,727
Loans and leases	4,282,968		4,135,625
Commercial Portfolio Segment [Member] | Asset Based Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0		0
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0		0
Financing Receivable, Recorded Investment, Nonaccrual Status	0		0
Financing Receivable, Recorded Investment, Current	861,203		805,306
Loans and leases	861,203		805,306
Commercial Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial and Industrial Sector [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,269		1,382
Commercial Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Asset Based Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0		0
Commercial Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial and Industrial Sector [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	648		577
Commercial Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Asset Based Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0		0
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans and leases	4,556,208		4,510,846		4,191,087
Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	543		662
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0		0
Financing Receivable, Recorded Investment, Nonaccrual Status	543		662
Financing Receivable, Recorded Investment, Current	361,312		374,398
Loans and leases	361,855		375,060
Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0		0
Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	0		0
Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	11,653		18,044
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0		0
Financing Receivable, Recorded Investment, Nonaccrual Status	10,637		9,871
Financing Receivable, Recorded Investment, Current	4,182,700		4,117,742
Loans and leases	4,194,353		4,135,786
Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	832		6,357
Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	184		1,816
Finance Leases Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,430		1,821
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0		0
Financing Receivable, Recorded Investment, Nonaccrual Status	547		225
Financing Receivable, Recorded Investment, Current	584,243		633,808
Loans and leases	585,673		635,629		$ 618,343
Finance Leases Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	883		903
Finance Leases Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 0		$ 693

[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.