SEC Schedule I - Summary of Investments - Other than Investments in Related Parties (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Summary of Investments, Other than Investments in Related Parties, Reportable Data Line Items
Summary of Investments, Other than Investments in Related Parties, Cost	$ 455,249
Summary of Investments, Other than Investments in Related Parties, Fair Value	233,052
US Government and Government Agencies and Authorities
Summary of Investments, Other than Investments in Related Parties, Reportable Data Line Items
Summary of Investments, Other than Investments in Related Parties, Cost	222,550
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	233,052
Obligations of U.S. states and political subdivisions
Summary of Investments, Other than Investments in Related Parties, Reportable Data Line Items
Summary of Investments, Other than Investments in Related Parties, Fair Value	491,183
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	491,183
All Other Corporate Bonds
Summary of Investments, Other than Investments in Related Parties, Reportable Data Line Items
Summary of Investments, Other than Investments in Related Parties, Cost	422,615
Summary of Investments, Other than Investments in Related Parties, Fair Value	441,318
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	441,318
Total fixed maturities
Summary of Investments, Other than Investments in Related Parties, Reportable Data Line Items
Summary of Investments, Other than Investments in Related Parties, Cost	1,100,414
Summary of Investments, Other than Investments in Related Parties, Fair Value	1,165,553
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	1,165,553
Industrial, Miscellaneous, and All Others
Summary of Investments, Other than Investments in Related Parties, Reportable Data Line Items
Summary of Investments, Other than Investments in Related Parties, Cost	21,237
Summary of Investments, Other than Investments in Related Parties, Fair Value	22,800
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	22,800
Total equity securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data Line Items
Summary of Investments, Other than Investments in Related Parties, Cost	21,237
Summary of Investments, Other than Investments in Related Parties, Fair Value	22,800
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	22,800
Totals
Summary of Investments, Other than Investments in Related Parties, Reportable Data Line Items
Summary of Investments, Other than Investments in Related Parties, Cost	1,121,651
Summary of Investments, Other than Investments in Related Parties, Fair Value	1,188,353
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	$ 1,188,353