Investment Securities - Credit Quality Indicator (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	$ 47,475	$ 40,927
State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	22,003	27,082
Other securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	1,175	$ 3,049
Aaa/AAA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	865
Aaa/AAA | Other securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	0
Aa/AA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	16,715
Aa/AA | Other securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	0
A | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	2,018
A | Other securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	0
Baa | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	426
Baa | Other securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	0
Not Rated | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	1,979
Not Rated | Other securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	1,175
Not Guaranteed or Pre-Refunded | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	14,706
Not Guaranteed or Pre-Refunded | Aaa/AAA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	865
Not Guaranteed or Pre-Refunded | Aa/AA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	11,270
Not Guaranteed or Pre-Refunded | A | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	960
Not Guaranteed or Pre-Refunded | Baa | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	0
Not Guaranteed or Pre-Refunded | Not Rated | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	1,611
Other Credit Enhancement or Insurance | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	7,297
Other Credit Enhancement or Insurance | Aaa/AAA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	0
Other Credit Enhancement or Insurance | Aa/AA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	5,445
Other Credit Enhancement or Insurance | A | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	1,058
Other Credit Enhancement or Insurance | Baa | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	426
Other Credit Enhancement or Insurance | Not Rated | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	368
Pre-Refunded | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	0
Pre-Refunded | Aaa/AAA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	0
Pre-Refunded | Aa/AA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	0
Pre-Refunded | A | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	0
Pre-Refunded | Baa | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	0
Pre-Refunded | Not Rated | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Net carrying amount	$ 0