Schedule I. Summary of Investments - Other than Investments in Related Parties (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	$ 2,917,983
Fair Value	3,171,328
Amounts at Which Shown in Balance Sheet	3,170,961
Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	2,788,326
Fair Value	2,860,345
Amounts at Which Shown in Balance Sheet	2,860,338
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	375,603
Fair Value	377,644
Amounts at Which Shown in Balance Sheet	377,644
States, Municipalities and Political Subdivisions [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	748,687
Fair Value	778,340
Amounts at Which Shown in Balance Sheet	778,340
Foreign Governments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	136,487
Fair Value	140,173
Amounts at Which Shown in Balance Sheet	140,173
Public Utilities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	206,366
Fair Value	212,357
Amounts at Which Shown in Balance Sheet	212,357
All Other Bonds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,317,149
Fair Value	1,347,081
Amounts at Which Shown in Balance Sheet	1,347,074
Redeemable Preferred Stock [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	4,034
Fair Value	4,750
Amounts at Which Shown in Balance Sheet	4,750
Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	75,359
Fair Value	249,909
Amounts at Which Shown in Balance Sheet	249,909
Public Utilities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	7,231
Fair Value	20,290
Amounts at Which Shown in Balance Sheet	20,290
Banks, Trusts and Insurance Companies [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	16,637
Fair Value	93,663
Amounts at Which Shown in Balance Sheet	93,663
Industrial, Miscellaneous and All Other [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	44,823
Fair Value	129,024
Amounts at Which Shown in Balance Sheet	129,024
Nonredeemable Preferred Stocks [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	6,668
Fair Value	6,932
Amounts at Which Shown in Balance Sheet	6,932
Mortgage Loans on Real Estate [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	4,199
Fair Value	4,559
Amounts at Which Shown in Balance Sheet	4,199
Policy Loans [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	5,916
Fair Value	5,916
Amounts at Which Shown in Balance Sheet	5,916
Other Long-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	44,008
Fair Value	50,424
Amounts at Which Shown in Balance Sheet	50,424
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