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]
Total investments and cash, Cost	$ 8,435,266
Total investments and cash, Market Value	9,075,466
Total investments and cash, Amount Shown In Balance Sheet	9,075,466
Fixed Maturities-Available For Sale [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	5,289,619
Total investments and cash, Market Value	5,531,410
Total investments and cash, Amount Shown In Balance Sheet	5,531,410
U.S. Government And Government Agencies [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	77,611
Total investments and cash, Market Value	78,190
Total investments and cash, Amount Shown In Balance Sheet	78,190
States, Municipalities And Political Subdivisions [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	1,214,990
Total investments and cash, Market Value	1,291,963
Total investments and cash, Amount Shown In Balance Sheet	1,291,963
Foreign Government Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	732,277
Total investments and cash, Market Value	780,003
Total investments and cash, Amount Shown In Balance Sheet	780,003
Foreign Corporate Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	990,671
Total investments and cash, Market Value	1,031,240
Total investments and cash, Amount Shown In Balance Sheet	1,031,240
Public Utilities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	79,235
Total investments and cash, Market Value	84,266
Total investments and cash, Amount Shown In Balance Sheet	84,266
All Other Corporate Bonds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	1,447,997
Total investments and cash, Market Value	1,499,221
Total investments and cash, Amount Shown In Balance Sheet	1,499,221
Mortgage-Backed Securities Commercial [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	45,157
Total investments and cash, Market Value	52,624
Total investments and cash, Amount Shown In Balance Sheet	52,624
Agency Residential [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	672,724
Total investments and cash, Market Value	683,722
Total investments and cash, Amount Shown In Balance Sheet	683,722
Non-agency Residential [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	1,933
Total investments and cash, Market Value	2,329
Total investments and cash, Amount Shown In Balance Sheet	2,329
Redeemable Preferred Stock [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	27,024
Total investments and cash, Market Value	27,852
Total investments and cash, Amount Shown In Balance Sheet	27,852
Fixed Maturities - Available For Sale, At Fair Value [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	41,068	[1]
Total investments and cash, Market Value	41,470	[1]
Total investments and cash, Amount Shown In Balance Sheet	41,470	[1]
Equity Securities - Available For Sale, At Market Value [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	15
Total investments and cash, Market Value	13
Total investments and cash, Amount Shown In Balance Sheet	13
Equity Securities - Available For Sale, At Fair Value [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	1,035,179	[1]
Total investments and cash, Market Value	1,199,848	[1]
Total investments and cash, Amount Shown In Balance Sheet	1,199,848	[1]
Short-Term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	465,550
Total investments and cash, Market Value	465,550
Total investments and cash, Amount Shown In Balance Sheet	465,550
Other Invested Assets [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	420,744
Total investments and cash, Market Value	420,744
Total investments and cash, Amount Shown In Balance Sheet	420,744
Other Invested Assets, At Fair Value [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	835,371	[1]
Total investments and cash, Market Value	1,068,711	[1]
Total investments and cash, Amount Shown In Balance Sheet	1,068,711	[1]
Cash [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments and cash, Cost	347,720
Total investments and cash, Market Value	347,720
Total investments and cash, Amount Shown In Balance Sheet	$ 347,720

[1] Original cost does not reflect adjustments, which have been realized through the statements of operations and comprehensive income.