Additional Information about Assets and Liabilities That Are Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 576,351
Change in fair value of financial instruments	17,345
Purchases	0
Principal Repayments	(70,125)
Ending Balance	523,571
Beginning Balance	296,165
Change in fair value of financial instruments	173,239
Purchases	0
Sales	0
Principal repayments	(85,706)
Ending Balance	383,698
Derivative Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	79,462
Change in fair value of financial instruments	(12,384)
Purchases	0
Sales	0
Principal repayments	0
Ending Balance	67,078
CDO notes payable, at fair value
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	187,048
Change in fair value of financial instruments	183,964
Purchases	0
Sales	0
Principal repayments	(66,325)
Ending Balance	304,687
Junior Subordinated Notes, at Fair Value
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	29,655
Change in fair value of financial instruments	1,659
Purchases	0
Sales	0
Principal repayments	(19,381)
Ending Balance	11,933
Trading Securities-TruPS and Subordinated Debentures
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	485,203
Change in fair value of financial instruments	18,786
Purchases	0
Principal Repayments	(17,000)
Ending Balance	486,989
Security-Related Receivables-TruPS and subordinated Debenture Receivables
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	91,148
Change in fair value of financial instruments	(1,441)
Purchases	0
Principal Repayments	(53,125)
Ending Balance	$ 36,582

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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)

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Amount of purchases 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)(2)

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Amount of settlement 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)(2)

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

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Fair value 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.

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Amount of purchases 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

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)(2)

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

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Amount of sales 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

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)(2)

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

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Amount of settlements 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

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)(2)

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

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