Fair Value Measurements - Recurring Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	$ 1,352,637	$ 1,298,587
Equity securities, at fair value	930	915
U.S. Treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	1,750	1,840
Obligations of U.S. Government sponsored entities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	313,428	372,488
Obligations of U.S. states and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	102,484	97,785
U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	174,515	164,451
U.S. Government sponsored entities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	758,027	659,590
U.S. corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	2,433	2,433
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	1,352,637	1,298,587
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | U.S. Treasuries | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | U.S. Treasuries | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	1,750	1,840
Recurring | U.S. Treasuries | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | Obligations of U.S. Government sponsored entities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | Obligations of U.S. Government sponsored entities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	313,428	372,488
Recurring | Obligations of U.S. Government sponsored entities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | Obligations of U.S. states and political subdivisions | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | Obligations of U.S. states and political subdivisions | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	102,484	97,785
Recurring | Obligations of U.S. states and political subdivisions | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | U.S. Government agencies | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | U.S. Government agencies | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	174,515	164,451
Recurring | U.S. Government agencies | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | U.S. Government sponsored entities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | U.S. Government sponsored entities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	758,027	659,590
Recurring | U.S. Government sponsored entities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | U.S. corporate debt securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | U.S. corporate debt securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	2,433	2,433
Recurring | U.S. corporate debt securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	0	0
Recurring | Equity securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, at fair value	0	0
Recurring | Equity securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, at fair value	0	0
Recurring | Equity securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, at fair value	930	915
Recurring | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	1,352,637	1,298,587
Recurring | Fair Value | U.S. Treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	1,750	1,840
Recurring | Fair Value | Obligations of U.S. Government sponsored entities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	313,428	372,488
Recurring | Fair Value | Obligations of U.S. states and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	102,484	97,785
Recurring | Fair Value | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	174,515	164,451
Recurring | Fair Value | U.S. Government sponsored entities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	758,027	659,590
Recurring | Fair Value | U.S. corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, fair value	2,433	2,433
Recurring | Fair Value | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, at fair value	$ 930	$ 915