Investment Securities - Credit Quality Indicator (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	$ 335,946	$ 40,927
State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	312,416	27,082
Other securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	1,176	$ 3,049
Aaa/AAA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	57,886
Aaa/AAA | Other securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	0
Aa/AA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	231,269
Aa/AA | Other securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	0
A | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	20,860
A | Other securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	0
Not Rated | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	2,401
Not Rated | Other securities
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	1,176
Not Guaranteed or Pre-Refunded | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	255,375
Not Guaranteed or Pre-Refunded | Aaa/AAA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	52,058
Not Guaranteed or Pre-Refunded | Aa/AA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	181,481
Not Guaranteed or Pre-Refunded | A | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	19,838
Not Guaranteed or Pre-Refunded | Not Rated | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	1,998
Other Credit Enhancement or Insurance | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	57,041
Other Credit Enhancement or Insurance | Aaa/AAA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	5,828
Other Credit Enhancement or Insurance | Aa/AA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	49,788
Other Credit Enhancement or Insurance | A | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	1,022
Other Credit Enhancement or Insurance | Not Rated | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	403
Pre-Refunded | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	0
Pre-Refunded | Aaa/AAA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	0
Pre-Refunded | Aa/AA | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	0
Pre-Refunded | A | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	0
Pre-Refunded | Not Rated | State and political subdivisions
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	$ 0