Fair Value Measurements (Narrative) (Details) (Fair Value Hierarchy, Level 3 [Member], USD $)	Sep. 30, 2013	Dec. 31, 2012
Fair Value Hierarchy, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Auction Rate Securities Available For Sale	$ 125,000,000
Financial Instruments, Owned, Principal Investments, at Fair Value	$ 64,507,000	$ 68,167,000

The fair value as of the balance sheet date of firm holdings in private equity, mezzanine, venture capital, merchant banking, real estate and special situations investments. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 320

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6475986&loc=d3e42546-110969

Name:	us-gaap_FinancialInstrumentsOwnedPrincipalInvestmentsAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant