Other Investments (Details) - Components of other investments (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Other Investments [Line Items]
Other investments	$ 1,219,879	$ 985,262
Alternative funds
Other Investments [Line Items]
Other investments	694,872	455,055
Arbitrage
Other Investments [Line Items]
Other investments	278,680	132,847
Directional
Other Investments [Line Items]
Other investments	254,616	228,544
Event driven
Other Investments [Line Items]
Other investments	96,451	0
Multi-style
Other Investments [Line Items]
Other investments	65,125	93,664
Private investment funds
Other Investments [Line Items]
Other investments	89,469	87,491
Overseas deposits
Other Investments [Line Items]
Other investments	96,117	91,425
Structured transactions
Other Investments [Line Items]
Other investments	312,122	323,705
Other
Other Investments [Line Items]
Other investments	$ 27,299	$ 27,586