Loans and Leases (Detail) - USD ($) $ in Thousands	Jun. 30, 2017		Dec. 31, 2016		Jun. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 17,273,678	[1],[2]	$ 17,026,588	[1],[2]	$ 16,272,029
Unamortized premiums	18,800		17,300
Pledged Financial Instruments, Not Separately Reported, Loans Receivable Pledged as Collateral	6,200,000
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	4,388,308		4,254,682		4,156,665
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	2,599,318		2,684,500		2,728,452
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	5,144,171		4,940,931		4,577,482
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	4,556,208		4,510,846		4,191,087
Finance Leases Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
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.