Investment Information - Other investments (Details) - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		$ 2,392,426	$ 2,088,763
Available for sale
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		248,661	167,970
Available for sale | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		114,594	84,778
Available for sale | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		52,266	33,923
Available for sale | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		14,632	7,469
Available for sale | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		67,169	41,800
Fair value option
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		2,143,765	1,920,793
Fair value option | Term loan investments
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		1,334,590	1,190,799
Other investments par		1,367,178	1,208,537
Fair value option | Mezzanine debt funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		141,066	127,943
Fair value option | Asian and emerging markets
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		245,866	178,568
Fair value option | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		86,389	75,468
Fair value option | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments		197,144	218,298
Fair value option | Other
Schedule Of Other Investments [Line Items]
Other investments and fair value option investments	[1]	$ 138,710	$ 129,717

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