Loans - Narrative (Details)	3 Months Ended
	Mar. 31, 2021 USD ($) contract loan	Mar. 31, 2020 USD ($) contract	Dec. 31, 2020 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable on loans	$ 15,500,000		$ 16,100,000
Net deferred loan fees	(12,900,000)		(10,000,000.0)
Overdraft balances included in home equity and consumer loans	220,000		650,000
Loans pledged for actual and potential borrowings at the Federal Home Loan Bank	$ 2,220,000,000		$ 2,280,000,000
Number of loans still accruing | loan	0		1
Financing receivable, 90 days or more past due, still accruing	$ 0		$ 1,000
Financing receivable, nonaccrual, in the process of foreclosure	1,600,000		1,700,000
Financing receivable, troubled debt restructuring	4,900,000		5,000,000.0
Financing receivable, accrual, troubled debt restructuring	3,800,000		3,900,000
Financing receivable nonaccrual troubled debt restructuring	$ 1,100,000		1,100,000
Financing receivable, modifications, number of contracts | contract	0	0
Financing receivable, troubled debt restructuring, subsequent default, number of contracts | contract	0
COVID-19
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, deferred	$ 0
Paycheck Protection Program ("PPP")
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, before allowance for credit loss and fee	346,200,000		284,600,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, 90 days or more past due, still accruing	$ 0		$ 1,000
Financing receivable, troubled debt restructuring, subsequent default, number of contracts | contract		2
Recorded investment		$ 83,000