Loan Portfolio and Credit Quality - Narrative (Details) $ in Millions	Mar. 31, 2021 USD ($) loan security	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged in blanket lien agreement	$ 2,200.0	$ 2,200.0
Loans pledged as collateral	320.7	332.8
TDRs	$ 14.0	13.9
Number of residential and home equity loans processed | loan	365
Mortgage payments processed	$ 220.0
Number of residential and home equity loans deferred | loan	47
Mortgage payments deferred	$ 20.0
Number of commercial and industrial loans processed | loan	85
Commercial and industrial loans processed	$ 125.0
Number of commercial and industrial loans deferred | security	4
Commercial and industrial loans deferred	$ 5.7
Deferred loan (fees)/costs	(2.1)	0.3
Performing Financial Instruments
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDRs	$ 7.1	$ 7.2