Loans - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) Contract loan	Sep. 30, 2019 USD ($) Contract	Sep. 30, 2020 USD ($) Contract loan	Sep. 30, 2019 USD ($) Contract	Apr. 24, 2020 USD ($)	Dec. 31, 2019 USD ($)
Loans And Leases Receivable Disclosure [Line Items]
Loans	$ 0		$ 0			$ 0
Accrued interest receivable	4,700,000		4,700,000			2,900,000
Nonaccrual	0		0			1,215,000
Loans >90 Days Past Due & Still Accruing	0		0
Recorded investment in troubled debt restructurings	330,000		330,000			333,000
Specific reserves to customers whose loan terms have been modified in TDRs	$ 330,000		$ 330,000			333,000
Loans identified as TDRs | Contract	0	0	0	0
Financing receivable, modifications, subsequent default, recorded investment	$ 0	$ 0	$ 0	$ 0
Loans aggregate balance	$ 1,077,480,000		$ 1,077,480,000			993,020,000
Paycheck Protection Program and Health Care Enhancement Act
Loans And Leases Receivable Disclosure [Line Items]
Number of loans originated | loan	978		978
Total loans funded	$ 66,300,000		$ 66,300,000
Additional funding under CARES act					$ 310,000,000,000
Home Mortgage
Loans And Leases Receivable Disclosure [Line Items]
Loans aggregate balance	126,143,000		126,143,000			$ 121,161,000
Payment Deferral
Loans And Leases Receivable Disclosure [Line Items]
Recorded investment in troubled debt restructurings	$ 229,933,000		$ 229,933,000
Number of processed loan deferments | loan	172		172
Number of loans | loan	130		130
Loans aggregate balance	$ 173,021,000		$ 173,021,000
Payment Deferral | Home Mortgage
Loans And Leases Receivable Disclosure [Line Items]
Recorded investment in troubled debt restructurings	$ 30,205,000		$ 30,205,000
Number of processed loan deferments | loan	69		69
Number of loans | loan	51		51
Loans aggregate balance	$ 22,344,000		$ 22,344,000