Loans and Leases (Summary Of Loan And Lease Portfolio Aging By Class Of Loan) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	$ 175,864		$ 179,403
90 or More Days Past Due and Accruing	749		2,051
Non-accrual	133,816		140,069
Current	16,850,724		15,492,332
Total Loans and Leases	17,026,588	[1],[2]	15,671,735	[1],[2]	$ 13,900,025
Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	58,519		71,298
90 or More Days Past Due and Accruing	0		2,029
Non-accrual	47,279		54,201
Current	4,196,163		3,989,703
Total Loans and Leases	4,254,682		4,061,001		3,509,175
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	2,684,500		2,702,560		2,549,401
Consumer Portfolio Segment [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	5,381		2,565
90 or More Days Past Due and Accruing	0		0
Non-accrual	1,663		560
Current	269,226		246,597
Total Loans and Leases	274,607		249,162
Consumer Portfolio Segment [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	50,539		50,640
90 or More Days Past Due and Accruing	0		0
Non-accrual	35,926		37,337
Current	2,359,354		2,402,758
Total Loans and Leases	2,409,893		2,453,398
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	4,940,931		4,315,999		3,749,270
Commercial Portfolio Segment [Member] | Commercial and Industrial Sector [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	40,898		31,115
90 or More Days Past Due and Accruing	749		22
Non-accrual	38,190		27,037
Current	4,094,727		3,531,669
Total Loans and Leases	4,135,625		3,562,784
Commercial Portfolio Segment [Member] | Asset Based Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	0		0
90 or More Days Past Due and Accruing	0		0
Non-accrual	0		0
Current	805,306		753,215
Total Loans and Leases	805,306		753,215
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	4,510,846		3,991,649		3,554,428
Commercial Real Estate Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	18,044		19,016
90 or More Days Past Due and Accruing	0		0
Non-accrual	9,871		16,767
Current	4,117,742		3,673,408
Total Loans and Leases	4,135,786		3,692,424
Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	662		3,461
90 or More Days Past Due and Accruing	0		0
Non-accrual	662		3,461
Current	374,398		295,764
Total Loans and Leases	375,060		299,225
Finance Leases Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	1,821		1,308
90 or More Days Past Due and Accruing	0		0
Non-accrual	225		706
Current	633,808		599,218
Total Loans and Leases	635,629		600,526		$ 537,751
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	28,337		23,751
Financing Receivables, 30 to 59 Days Past Due [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	8,631		10,365
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	2,233		1,390
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	8,831		9,061
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial and Industrial Sector [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	1,382		768
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Asset Based Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	0		0
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	6,357		1,624
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	0		0
Financing Receivables, 30 to 59 Days Past Due [Member] | Finance Leases Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	903		543
Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	12,962		13,532
Financing Receivables, 60 to 89 Days Past Due [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	2,609		4,703
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	1,485		615
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	5,782		4,242
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Commercial and Industrial Sector [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	577		3,288
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Portfolio Segment [Member] | Asset Based Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	0		0
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	1,816		625
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	0		0
Financing Receivables, 60 to 89 Days Past Due [Member] | Finance Leases Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-accrual	$ 693		$ 59

[1] At December 31, 2016, the Company had pledged $6.4 billion of eligible loans as collateral to support borrowing capacity at the FHLB of Boston and the FRB of Boston.

[2] Loans and leases include net deferred fees and net premiums and discounts of $17.3 million and $18.0 million at December 31, 2016 and December 31, 2015, respectively.