Commitments and Contingencies (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) sublease	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Loan commitments
Unadvanced portion of loans and leases	$ 585,295		$ 585,295		$ 648,291
Unused lines of credit:
Home equity	328,116		328,116		280,786
Other consumer	14,476		14,476		12,383
Other commercial	188		188		529
Unused letters of credit:
Financial standby letters of credit	10,978		10,978		12,389
Performance standby letters of credit	472		472		392
Commercial and similar letters of credit	1,717		1,717		821
Back-to-back interest-rate swaps (Notional principal amounts)	747,233		747,233		490,632
Unfunded credit commitments liability included in other liabilities	1,300	$ 1,400	1,300	$ 1,400	1,300
Fair value of interest rate swap assets	24,800		24,800		8,700
Fair value of interest rate swap liabilities	24,800		24,800		8,800
Summary of future minimum rental payments under noncancelable operating leases year ending December 31
Remainder of 2016	1,283		1,283
Year ending:
2017	4,919		4,919
2018	4,563		4,563
2019	3,712		3,712
2020	3,155		3,155
2021	2,646		2,646
Thereafter	11,993		11,993
Total	32,271		32,271
Total rental expense	1,300	$ 1,400	$ 3,900	$ 4,000
Number of new sublease agreements | sublease			2
Minimum
Summary of future minimum rental payments under noncancelable operating leases year ending December 31
Lease term (over 20 years)			5 years
Maximum
Summary of future minimum rental payments under noncancelable operating leases year ending December 31
Lease term (over 20 years)			25 years
Commercial real estate
Loan commitments
Commitments to originate loans and leases	68,304		$ 68,304		36,000
Commercial
Loan commitments
Commitments to originate loans and leases	74,655		74,655		78,017
Residential mortgage
Loan commitments
Commitments to originate loans and leases	$ 5,019		$ 5,019		$ 19,430