Fair Value Measurements (Details) | 12 Months Ended |
Dec. 31, 2019USD ($) | Dec. 31, 2018USD ($) |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | $ 16,033,000 | $ 15,068,000 |
Assets, Fair Value Disclosure | 1,393,992,000 | 1,246,107,000 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 | 0 | 0 |
Fair Value Measurement with Unobservable Inputs reconciliation, Recurring Basis, Asset, Transfers into Level 3 | $ 0 | 0 |
Percent of Level 2 Debt Maturity to Total Reported Fair Value of Financial Assets | 98.00% | |
Number of Material Changes to Investment Valuation Method or Assumptions | 0 | |
Number of Third Party Pricing Changes | 0 | |
Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, Fair Value Disclosure | $ 27,433,000 | 26,389,000 |
Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, Fair Value Disclosure | 1,366,559,000 | 1,219,718,000 |
Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets, Fair Value Disclosure | 0 | 0 |
US Treasury and Government [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 15,878,000 | 15,554,000 |
US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 11,348,000 | 11,274,000 |
US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 4,530,000 | 4,280,000 |
US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
US States and Political Subdivisions Debt Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 536,284,000 | 720,115,000 |
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 536,284,000 | 720,115,000 |
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Corporate Debt Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 650,088,000 | 381,796,000 |
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 52,000 | 47,000 |
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 650,036,000 | 381,749,000 |
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Commercial Mortgage Backed Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 1,100,000 | 40,014,000 |
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 1,100,000 | 40,014,000 |
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Residential Mortgage Backed Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 130,287,000 | 68,684,000 |
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 130,287,000 | 68,684,000 |
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Asset-backed Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 44,203,000 | 4,757,000 |
Asset-backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Asset-backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 44,203,000 | 4,757,000 |
Asset-backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Foreign Governments [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 119,000 | 119,000 |
Foreign Governments [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Foreign Governments [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 119,000 | 119,000 |
Foreign Governments [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Debt Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 1,377,959,000 | 1,231,039,000 |
Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 11,400,000 | 11,321,000 |
Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 1,366,559,000 | 1,219,718,000 |
Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Stock Mutual Funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 3,274,000 | 2,906,000 |
Stock Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 3,274,000 | 2,906,000 |
Stock Mutual Funds [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 0 | 0 |
Stock Mutual Funds [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 0 | 0 |
Bond Mutual Funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 12,311,000 | 11,774,000 |
Bond Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 12,311,000 | 11,774,000 |
Bond Mutual Funds [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 0 | 0 |
Bond Mutual Funds [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 0 | 0 |
Common Stock [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 134,000 | 94,000 |
Common Stock [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 134,000 | 94,000 |
Common Stock [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 0 | 0 |
Common Stock [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 0 | 0 |
Nonredeemable Preferred Stock [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 314,000 | 294,000 |
Nonredeemable Preferred Stock [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 314,000 | 294,000 |
Nonredeemable Preferred Stock [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 0 | 0 |
Nonredeemable Preferred Stock [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 0 | 0 |
Equity Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 16,033,000 | 15,068,000 |
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 16,033,000 | 15,068,000 |
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | 0 | 0 |
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Equity securities | $ 0 | $ 0 |