Derivative Instruments (Schedule Of Derivative Fair Values On Condensed Consolidated Balance Sheets) (Details) (USD $) In Thousands	Sep. 30, 2011		Dec. 31, 2010
Investment Portfolio [Member]
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	$ 881,103
Asset Derivative Fair Value	3,208
Liability Derivative Notional Amount	958,298
Liability Derivative Fair Value	15,440
Investment Portfolio [Member] | Foreign Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	74,853	[1]
Asset Derivative Fair Value	1,487	[1]
Liability Derivative Notional Amount	62,198	[1]
Liability Derivative Fair Value	6,989	[1]
Investment Portfolio [Member] | Interest Rate Futures [Member]
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	806,250	[1]
Asset Derivative Fair Value	1,721	[1]
Liability Derivative Notional Amount	896,100	[1]
Liability Derivative Fair Value	8,451	[1]
Operating Activities [Member]
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	934,808		26,758
Asset Derivative Fair Value	5,759		858
Liability Derivative Notional Amount	1,081,171		51,308
Liability Derivative Fair Value	26,878		1,629
Operating Activities [Member] | Foreign Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	53,705	[2]	26,758	[2]
Asset Derivative Fair Value	2,551	[2]	858	[2]
Liability Derivative Notional Amount	122,873	[2]	51,308	[2]
Liability Derivative Fair Value	$ 11,438	[2]	$ 1,629	[2]

[1] Asset and liability derivatives relating to the investment portfolio are classified within "balances receivable on sale of investments" or "balances due on purchases of investments" on the consolidated balance sheets.

[2] Asset and liability derivatives relating to operating activities are classified within "other assets" or "accounts payable and accrued liabilities" on the consolidated balance sheets.