Schedule I 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]
Summary of Investments, Other than Investments in Related Parties, Cost	$ 5,088,298
Summary of Investments, Other than Investments in Related Parties, Fair Value	5,161,122
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	5,152,418
US Government and Government Agencies and Authorities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	4,969
Summary of Investments, Other than Investments in Related Parties, Fair Value	5,305
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	5,305
US States and Political Subdivisions Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	18,601	[1]
Summary of Investments, Other than Investments in Related Parties, Fair Value	18,671	[1]
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	18,674	[1]
All Other Corporate Bonds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	15,618
Summary of Investments, Other than Investments in Related Parties, Fair Value	16,369
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	16,369
Residential Mortgage Backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	50
Summary of Investments, Other than Investments in Related Parties, Fair Value	51
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	51
Other investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	922
Summary of Investments, Other than Investments in Related Parties, Fair Value	976
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	976
Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	40,160
Summary of Investments, Other than Investments in Related Parties, Fair Value	41,372
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	41,375
Trading Assets, Excluding Debt and Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	4,057,252
Summary of Investments, Other than Investments in Related Parties, Fair Value	4,094,622
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	4,094,622
Common Stocks, by Industry [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	77,758
Summary of Investments, Other than Investments in Related Parties, Fair Value	100,357
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	100,357
Nonredeemable Preferred Stock [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	10,502
Summary of Investments, Other than Investments in Related Parties, Fair Value	11,782
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	11,782
Equity Securities, Investment Summary [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	88,260
Summary of Investments, Other than Investments in Related Parties, Fair Value	112,139
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	112,139
Short-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	777,534
Summary of Investments, Other than Investments in Related Parties, Fair Value	777,532
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	777,532
Other Long-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	125,092
Summary of Investments, Other than Investments in Related Parties, Fair Value	135,457
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	$ 126,750

[1] Held to maturity and available for sale.