Summary of Total Recourse and Non-Recourse Indebtedness (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2013		Dec. 31, 2012
Debt Instrument [Line Items]
Unpaid Principal Balance	$ 2,545,805		$ 2,612,362
Carrying Amount	1,919,620		1,799,595
Weighted- Average Interest Rate	1.30%		1.40%
Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	193,286	[1]	186,242	[2]
Carrying Amount	181,985	[1]	172,476	[2]
Weighted- Average Interest Rate	5.00%	[1]	5.90%	[2]
Non-recourse indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	2,352,519		2,426,120
Carrying Amount	1,737,635		1,627,119
Weighted- Average Interest Rate	1.00%		1.10%
7.0% convertible senior notes | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	115,000	[3]	115,000	[3]
Carrying Amount	110,437	[3]	109,631	[3]
Weighted- Average Interest Rate	7.00%	[3]	7.00%	[3]
Contractual Maturity, month and year	2031-04	[3]	2031-04	[3]
Secured credit facility | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	7,121		8,090
Carrying Amount	7,121		8,090
Weighted- Average Interest Rate	3.00%		3.00%
Contractual Maturity, month and year	2016-12		2016-12
Junior subordinated notes, at fair value | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	18,671	[4]	38,052	[4]
Carrying Amount	11,933	[4]	29,655	[4]
Weighted- Average Interest Rate	0.50%	[4]	5.20%	[4]
Contractual Maturity, month and year	2035-03	[4]
Junior subordinated notes, at fair value | Minimum | Recourse Indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year			2015-10	[4]
Junior subordinated notes, at fair value | Maximum | Recourse Indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year			2035-03	[4]
Junior subordinated notes, at amortized cost | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	25,100		25,100
Carrying Amount	25,100		25,100
Weighted- Average Interest Rate	2.80%		2.80%
Contractual Maturity, month and year	2037-04		2037-04
CDO notes payable, at amortized cost | Non-recourse indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	1,290,484	[5],[6]	1,297,069	[5],[7]
Carrying Amount	1,288,968	[5],[6]	1,295,400	[5],[7]
Weighted- Average Interest Rate	0.60%	[5],[6]	0.60%	[5],[7]
CDO notes payable, at amortized cost | Minimum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, year	2045	[5],[6]	2045	[5],[7]
CDO notes payable, at amortized cost | Maximum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, year	2046	[5],[6]	2046	[5],[7]
CDO notes payable, at fair value | Non-recourse indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	918,055	[4],[5],[8]	984,380	[4],[5],[9]
Carrying Amount	304,687	[4],[5],[8]	187,048	[4],[5],[9]
Weighted- Average Interest Rate	1.00%	[4],[5],[8]	1.00%	[4],[5],[9]
CDO notes payable, at fair value | Minimum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, year	2037	[4],[5],[8]	2037	[4],[5],[9]
CDO notes payable, at fair value | Maximum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, year	2038	[4],[5],[8]	2038	[4],[5],[9]
Loans payable on real estate | Non-recourse indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	143,980		144,671
Carrying Amount	143,980		144,671
Weighted- Average Interest Rate	5.40%		5.40%
Loans payable on real estate | Minimum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year	2015-09		2015-09
Loans payable on real estate | Maximum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year	2022-11		2021-05
CMBS Facilities
Debt Instrument [Line Items]
Carrying Amount	1,760,167
CMBS Facilities | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	12,569
Carrying Amount	12,569
Weighted- Average Interest Rate	2.70%
CMBS Facilities | Minimum | Recourse Indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year	2013-10
CMBS Facilities | Maximum | Recourse Indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year	2013-11
Commercial mortgage facility | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	14,825
Carrying Amount	$ 14,825
Weighted- Average Interest Rate	2.20%
Contractual Maturity, month and year	2013-12

[1] Excludes senior secured notes issued by us with an aggregate principal amount equal to $90,000 with a weighted average coupon of 7.0%, which are eliminated in consolidation.

[2] Excludes senior secured notes issued by us with an aggregate principal amount equal to $94,000 with a weighted average coupon of 7.0%, which are eliminated in consolidation.

[3] Our 7.0% convertible senior notes are redeemable at par, at the option of the holder, in April 2016, April 2021, and April 2026.

[4] Relates to liabilities which we elected to record at fair value under FASB ASC Topic 825.

[5] Excludes CDO notes payable purchased by us which are eliminated in consolidation.

[6] Collateralized by $1,760,167 principal amount of commercial mortgages, mezzanine loans, other loans, and preferred equity interests. These obligations were issued by separate legal entities and consequently the assets of the special purpose entities that collateralize these obligations are not available to our creditors.

[7] Collateralized by $1,757,789 principal amount of commercial mortgages, mezzanine loans, other loans and preferred equity interests. These obligations were issued by separate legal entities and consequently the assets of the special purpose entities that collateralize these obligations are not available to our creditors.

[8] Collateralized by $1,035,821 principal amount of investments in securities and security-related receivables and loans, before fair value adjustments. The fair value of these investments as of June 30, 2013 was $791,642. These obligations were issued by separate legal entities and consequently the assets of the special purpose entities that collateralize these obligations are not available to our creditors.

[9] Collateralized by $1,118,346 principal amount of investments in securities and security-related receivables and loans, before fair value adjustments. The fair value of these investments as of December 31, 2012 was $849,919. These obligations were issued by separate legal entities and consequently the assets of the special purpose entities that collateralize these obligations are not available to our creditors.