Fair Value Measurements - Recurring and Nonrecurring (Details) - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	$ 544,502,000			$ 470,746,000
Equity securities	7,655,000			7,472,000
Available-for-sale debt securities	544,502,000			470,746,000
Financing receivable, allowance for credit loss	13,937,000	$ 9,405,000	$ 10,546,000	9,130,000	$ 9,118,000	$ 9,104,000
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	7,655,000			7,472,000
Available-for-sale debt securities	544,502,000			470,746,000
Loans, net	1,111,954,000			934,250,000
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	7,655,000			7,472,000
Available-for-sale debt securities	544,502,000			470,746,000
Loans, net	1,098,205,000			928,807,000
Loans, charge-offs	0	$ 0
U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	41,706,000			14,494,000
Obligations of states and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	229,855,000			91,111,000
U.S. Government sponsored entities and agencies collateralized by residential mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	201,837,000			196,719,000
Private label mortgage and asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	52,501,000			159,378,000
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	18,603,000			9,044,000
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	0			0
Loans, net	0			0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	544,502,000			470,746,000
Loans, net	0			0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	0			0
Loans, net	1,098,205,000			928,807,000
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	552,157,000			478,218,000
Recurring | U.S. Government agencies | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	41,706,000			14,494,000
Recurring | Obligations of states and political subdivisions | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	229,855,000			91,111,000
Recurring | U.S. Government sponsored entities and agencies collateralized by residential mortgage obligations | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	201,837,000			196,719,000
Recurring | Private label mortgage and asset backed securities | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	52,501,000			159,378,000
Recurring | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities				9,044,000
Recurring | Corporate debt securities | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	18,603,000
Recurring | Other equity securities | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	7,655,000			7,472,000
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	7,655,000			7,472,000
Recurring | Level 1 | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0			0
Recurring | Level 1 | Obligations of states and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0			0
Recurring | Level 1 | U.S. Government sponsored entities and agencies collateralized by residential mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0			0
Recurring | Level 1 | Private label mortgage and asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0			0
Recurring | Level 1 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0			0
Recurring | Level 1 | Other equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	7,655,000			7,472,000
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	544,502,000			470,746,000
Recurring | Level 2 | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	41,706,000			14,494,000
Recurring | Level 2 | Obligations of states and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	229,855,000			91,111,000
Recurring | Level 2 | U.S. Government sponsored entities and agencies collateralized by residential mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	201,837,000			196,719,000
Recurring | Level 2 | Private label mortgage and asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	52,501,000			159,378,000
Recurring | Level 2 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	18,603,000			9,044,000
Recurring | Level 2 | Other equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0			0
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	0			0
Recurring | Level 3 | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0			0
Recurring | Level 3 | Obligations of states and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0			0
Recurring | Level 3 | U.S. Government sponsored entities and agencies collateralized by residential mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0			0
Recurring | Level 3 | Private label mortgage and asset backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0			0
Recurring | Level 3 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0			0
Recurring | Level 3 | Other equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0			0
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value disclosure	0			$ 0
Nonrecurring | Carrying Amount | Impaired Financing Receivable [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, net	190,000
Nonrecurring | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	166
Financing receivable, allowance for credit loss	24,000
Nonrecurring | Fair Value | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, net	166
Nonrecurring | Fair Value | Impaired Financing Receivable [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, net	166,000
Nonrecurring | Level 1 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	0
Nonrecurring | Level 1 | Fair Value | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, net	0
Nonrecurring | Level 2 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	0
Nonrecurring | Level 2 | Fair Value | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, net	0
Nonrecurring | Level 3 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value	166
Nonrecurring | Level 3 | Fair Value | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, net	$ 166