Schedule I. Summary of Investments - Other than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2018 USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	$ 1,900,465
Fair Value	2,074,362
Amounts at Which Shown in Balance Sheet	2,074,123
Fixed Maturities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	1,772,566
Fair Value	1,762,728
Amounts at Which Shown in Balance Sheet	1,762,728
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	243,167
Fair Value	242,100
Amounts at Which Shown in Balance Sheet	242,100
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	939,068
Fair Value	936,060
Amounts at Which Shown in Balance Sheet	936,060
Foreign governments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	9,698
Fair Value	9,716
Amounts at Which Shown in Balance Sheet	9,716
Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	56,808
Fair Value	56,059
Amounts at Which Shown in Balance Sheet	56,059
All other bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	520,803
Fair Value	516,044
Amounts at Which Shown in Balance Sheet	516,044
Redeemable preferred stock
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	3,022
Fair Value	2,749
Amounts at Which Shown in Balance Sheet	2,749
Equity Securities [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	64,819
Fair Value	248,361
Amounts at Which Shown in Balance Sheet	248,361
Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	4,226
Fair Value	15,949
Amounts at Which Shown in Balance Sheet	15,949
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	13,737
Fair Value	101,555
Amounts at Which Shown in Balance Sheet	101,555
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	41,430
Fair Value	125,206
Amounts at Which Shown in Balance Sheet	125,206
Nonredeemable preferred stocks
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	5,426
Fair Value	5,651
Amounts at Which Shown in Balance Sheet	5,651
Mortgage loans
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	25,828
Fair Value	26,021
Amounts at Which Shown in Balance Sheet	25,782
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	37,077
Fair Value	37,077
Amounts at Which Shown in Balance Sheet	37,077
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