Schedule 1 Summary of Investments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 6,513,703
Amount shown in Balance Sheet	6,950,398
Available For Sale Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	5,856,432
Fair Value	6,281,781
Amount shown in Balance Sheet	6,281,781
US Government Agencies Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	195,049
Fair Value	199,607
Amount shown in Balance Sheet	199,607
US States and Political Subdivisions Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	969,966
Fair Value	1,065,811
Amount shown in Balance Sheet	1,065,811
Special Purpose Revenue Bonds Of States Municipalities And Political Subdivisions [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,033,947
Fair Value	2,200,331
Amount shown in Balance Sheet	2,200,331
Corporate Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,247,282
Fair Value	1,315,170
Amount shown in Balance Sheet	1,315,170
Residential Mortgage Backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	632,665
Fair Value	664,887
Amount shown in Balance Sheet	664,887
Commercial Mortgage Backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	482,808
Fair Value	524,289
Amount shown in Balance Sheet	524,289
Asset-backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	32,801
Fair Value	33,275
Amount shown in Balance Sheet	33,275
Foreign Government Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	261,914
Fair Value	278,411
Amount shown in Balance Sheet	278,411
Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	294,218
Fair Value	305,564
Amount shown in Balance Sheet	305,564
Banks, Trust and Insurance, Equities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	33,624
Fair Value	37,088
Amount shown in Balance Sheet	37,088
Industrial, Miscellaneous, and All Others [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	260,594
Fair Value	268,476
Amount shown in Balance Sheet	268,476
Short Term Investments Schedule One [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	363,053
Amount shown in Balance Sheet	$ 363,053