Schedule I. Summary of Investments - Other than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2016 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	$ 3,032,850
Fair Value	3,265,850
Amounts at Which Shown in Balance Sheet	3,265,660
Fixed Maturities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	2,900,757
Fair Value	2,912,715
Amounts at Which Shown in Balance Sheet	2,912,714
United States Government and government agencies and authorities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	99,908
Fair Value	100,792
Amounts at Which Shown in Balance Sheet	100,792
States, municipalities and political subdivisions
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,061,621
Fair Value	1,051,958
Amounts at Which Shown in Balance Sheet	1,051,958
Foreign governments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	62,995
Fair Value	65,234
Amounts at Which Shown in Balance Sheet	65,234
Public utilities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	212,360
Fair Value	215,674
Amounts at Which Shown in Balance Sheet	215,674
All other bonds
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,462,594
Fair Value	1,477,753
Amounts at Which Shown in Balance Sheet	1,477,752
Redeemable preferred stock
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,279
Fair Value	1,304
Amounts at Which Shown in Balance Sheet	1,304
Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	73,938
Fair Value	276,060
Amounts at Which Shown in Balance Sheet	276,060
Public utilities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	6,995
Fair Value	20,284
Amounts at Which Shown in Balance Sheet	20,284
Banks, trusts and insurance companies
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	17,493
Fair Value	116,156
Amounts at Which Shown in Balance Sheet	116,156
Industrial, miscellaneous and all other
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	46,431
Fair Value	136,451
Amounts at Which Shown in Balance Sheet	136,451
Nonredeemable preferred stocks
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	3,019
Fair Value	3,169
Amounts at Which Shown in Balance Sheet	3,169
Mortgage loans on real estate
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	3,706
Fair Value	3,895
Amounts at Which Shown in Balance Sheet	3,706
Policy loans
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	5,366
Fair Value	5,366
Amounts at Which Shown in Balance Sheet	5,366
Other long-term investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	48,908
Fair Value	67,639
Amounts at Which Shown in Balance Sheet	67,639
Short-term investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	175
Fair Value	175
Amounts at Which Shown in Balance Sheet	$ 175