Schedule I. Summary of Investments - Other than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2019 USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	$ 1,855,217
Fair Value	2,156,643
Amounts at Which Shown in Balance Sheet	2,155,099
Fixed Maturities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	1,671,701
Fair Value	1,734,863
Amounts at Which Shown in Balance Sheet	1,734,863
United States Government and government agencies and authorities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	167,262
Fair Value	169,693
Amounts at Which Shown in Balance Sheet	169,693
States, municipalities and political subdivisions
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	888,137
Fair Value	926,329
Amounts at Which Shown in Balance Sheet	926,329
Foreign governments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	4,936
Fair Value	5,117
Amounts at Which Shown in Balance Sheet	5,117
Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	60,950
Fair Value	63,651
Amounts at Which Shown in Balance Sheet	63,651
All other bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	546,502
Fair Value	565,986
Amounts at Which Shown in Balance Sheet	565,986
Redeemable preferred stock
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	3,914
Fair Value	4,087
Amounts at Which Shown in Balance Sheet	4,087
Equity Securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	67,529
Fair Value	299,203
Amounts at Which Shown in Balance Sheet	299,203
Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	3,760
Fair Value	16,295
Amounts at Which Shown in Balance Sheet	16,295
Banks, trusts and insurance companies
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	14,478
Fair Value	127,780
Amounts at Which Shown in Balance Sheet	127,780
Industrial, miscellaneous and all other
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	43,309
Fair Value	148,454
Amounts at Which Shown in Balance Sheet	148,454
Nonredeemable preferred stocks
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	5,982
Fair Value	6,674
Amounts at Which Shown in Balance Sheet	6,674
Mortgage loans
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	42,520
Fair Value	43,992
Amounts at Which Shown in Balance Sheet	42,448
Other long-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	73,292
Fair Value	78,410
Amounts at Which Shown in Balance Sheet	78,410
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	175
Fair Value	175
Amounts at Which Shown in Balance Sheet	$ 175