Realized and Unrealized Gains and Losses on Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Change in fair value of financial instruments, Assets			$ 17,345
Change in fair value of financial instruments, Liabilities			173,239
Change in fair value of financial instruments	(76,020)	(11,169)	(175,777)	(120,092)
Trading securities and security-related receivables
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Change in fair value of financial instruments, Assets	3,053	11,712	18,166	17,844
Collateralized Debt Obligations Notes Payable and Other Liabilities
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Change in fair value of financial instruments, Liabilities	(80,393)	(11,524)	(190,267)	(119,828)
Derivative
Fair Value Assets And Liabilities Measured On Unobservable Inputs [Line Items]
Change in fair value of financial instruments, Liabilities	$ 1,320	$ (11,357)	$ (3,676)	$ (18,108)

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Amount of increase (decrease) of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258

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- Definition

Amount of increase (decrease) of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of investments, not including unrealized gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, held at each balance sheet date and included in earnings for the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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