Investment Information (Other Investments) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	$ 1,281,781		$ 1,077,251
Available for sale
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	569,407		549,280
Available for sale | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	343,535		316,860
Available for sale | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	219,068		220,410
Available for sale | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	6,804		12,010
Fair value option
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	712,374		527,971
Fair value option | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	28,932		24,035
Fair value option | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	74,320		67,624
Fair value option | Non-investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	9,331		11,093
Fair value option | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	118,018	[1]	116,623	[1]
Fair value option | Term loan investments
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	481,773		308,596
Other investments par	$ 475,397		$ 307,016

[1] Includes fund investments with strategies in mortgage servicing rights, transportation and infrastructure assets and other.