Investment Information (Other Investments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	$ 1,123,122	$ 1,077,251
Available for sale
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	585,277	549,280
Available for sale | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	328,652	316,860
Available for sale | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	249,345	220,410
Available for sale | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	7,280	12,010
Fair value option
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	537,845	527,971
Fair value option | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	30,796	24,035
Fair value option | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	81,583	67,624
Fair value option | Non-investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	11,107	11,093
Fair value option | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	86,105	116,623
Fair value option | Term loan investments
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	328,254	308,596
Other investments par	$ 323,833	$ 307,016