Schedule I. Summary of Investments - Other than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2020 USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	$ 1,891,061
Fair Value	2,150,540
Amounts at Which Shown in Balance Sheet	2,149,217
Fixed Maturities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	1,720,291
Fair Value	1,825,443
Amounts at Which Shown in Balance Sheet	1,825,438
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	209,983
Fair Value	214,456
Amounts at Which Shown in Balance Sheet	214,456
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	824,545
Fair Value	884,700
Amounts at Which Shown in Balance Sheet	884,700
Foreign governments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	27,799
Fair Value	29,602
Amounts at Which Shown in Balance Sheet	29,602
Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	76,114
Fair Value	83,502
Amounts at Which Shown in Balance Sheet	83,502
All other bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	581,850
Fair Value	613,183
Amounts at Which Shown in Balance Sheet	613,178
Redeemable preferred stock
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	0
Fair Value	0
Amounts at Which Shown in Balance Sheet	0
Equity Securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	49,085
Fair Value	206,685
Amounts at Which Shown in Balance Sheet	206,685
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	16,320
Amounts at Which Shown in Balance Sheet	16,320
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	7,853
Fair Value	69,577
Amounts at Which Shown in Balance Sheet	69,577
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	36,877
Fair Value	120,193
Amounts at Which Shown in Balance Sheet	120,193
Nonredeemable preferred stocks
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	595
Fair Value	595
Amounts at Which Shown in Balance Sheet	595
Mortgage loans on real estate
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	47,690
Fair Value	48,932
Amounts at Which Shown in Balance Sheet	47,614
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	73,820
Fair Value	69,305
Amounts at Which Shown in Balance Sheet	69,305
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