Loan Portfolio and Credit Quality - Narrative (Details) $ in Thousands	Jun. 30, 2020 USD ($)	Jun. 30, 2020 loan	Jun. 30, 2020 security	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, 90 days or more past due, still accruing (less than)	$ 100
Loans pledged in blanket lien agreement	2,300,000			$ 2,500,000
Loans pledged as collateral	358,200			395,300
TDRs	14,800			12,600
Number of residential and home equity loans deferred		336	336
Mortgage payments deferred	214,500
Deferred loan (fees)/costs	(1,600)			8,100
Performing Financial Instruments
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDRs	$ 8,900			$ 7,100