Derivative Instruments (Location and Amounts of Derivative Fair Values On The Condensed Consolidated Balance Sheets) (Details) (Derivatives not designated as hedging instruments [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	$ 524,084		$ 776,273
Asset Derivative Fair Value	3,997		3,343
Liability Derivative Notional Amount	258,512		631,533
Liability Derivative Fair Value	5,185		12,401
Put options [Member] | Equity securities trading, at fair value [Member]
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	0	[1]	4,461	[1]
Asset Derivative Fair Value	0	[1]	336	[1]
Liability Derivative Notional Amount	0	[1]	0	[1]
Liability Derivative Fair Value	0	[1]	0	[1]
Foreign exchange contracts [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	95,884	[2]	91,162	[2]
Asset Derivative Fair Value	2,436	[2]	2,030	[2]
Foreign exchange contracts [Member] | Accounts payable and accrued liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivative Notional Amount	181,612	[2]	339,533	[2]
Liability Derivative Fair Value	3,103	[2]	8,934	[2]
Interest rate futures [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	428,200	[2]	680,650	[2]
Asset Derivative Fair Value	1,561	[2]	977	[2]
Interest rate futures [Member] | Accounts payable and accrued liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivative Notional Amount	76,900	[2]	292,000	[2]
Liability Derivative Fair Value	$ 2,082	[2]	$ 3,467	[2]

[1] Asset and liability derivatives relating to the put options are classified within "equity securities trading, at fair value" on the consolidated balance sheets.

[2] All other asset and liability derivatives are classified within "other assets" or "accounts payable and accrued liabilities" on the consolidated balance sheets.