Schedule I. Summary of Investments - Other than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	$ 2,934,284
Fair Value	3,143,039
Amounts at Which Shown in Balance Sheet	3,142,760
Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	2,805,216
Fair Value	2,838,258
Amounts at Which Shown in Balance Sheet	2,838,255
United States Government and Government Agencies and Authorities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	254,395
Fair Value	254,679
Amounts at Which Shown in Balance Sheet	254,679
States, Municipalities and Political Subdivisions [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	846,009
Fair Value	872,287
Amounts at Which Shown in Balance Sheet	872,287
Foreign Governments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	82,580
Fair Value	82,528
Amounts at Which Shown in Balance Sheet	82,528
Public Utilities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	213,233
Fair Value	215,683
Amounts at Which Shown in Balance Sheet	215,683
All Other Bonds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,406,431
Fair Value	1,410,596
Amounts at Which Shown in Balance Sheet	1,410,593
Redeemable Preferred Stock [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	2,568
Fair Value	2,485
Amounts at Which Shown in Balance Sheet	2,485
Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	72,957
Fair Value	240,600
Amounts at Which Shown in Balance Sheet	240,600
Public Utilities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	7,231
Fair Value	19,060
Amounts at Which Shown in Balance Sheet	19,060
Banks, Trusts and Insurance Companies [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	17,615
Fair Value	95,923
Amounts at Which Shown in Balance Sheet	95,923
Industrial, Miscellaneous and All Other [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	46,031
Fair Value	123,416
Amounts at Which Shown in Balance Sheet	123,416
Nonredeemable Preferred Stocks [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	2,080
Fair Value	2,201
Amounts at Which Shown in Balance Sheet	2,201
Mortgage Loans on Real Estate [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	3,961
Fair Value	4,237
Amounts at Which Shown in Balance Sheet	3,961
Policy Loans [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	5,618
Fair Value	5,618
Amounts at Which Shown in Balance Sheet	5,618
Other Long-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	46,357
Fair Value	54,151
Amounts at Which Shown in Balance Sheet	54,151
Short-term Investments [Member]
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