Summary of Total Recourse and Non-Recourse Indebtedness (Detail) - USD ($) $ in Thousands		9 Months Ended		12 Months Ended
		Sep. 30, 2016		Dec. 31, 2015		Apr. 30, 2016
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 2,012,582		$ 2,452,567
Unamortized Discount/Premium and Deferred Financing Costs		(36,719)		(53,092)
Indebtedness		$ 1,975,863		$ 2,399,475		$ 17,696
Weighted-Average Interest Rate		3.20%		2.70%
Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 532,308		$ 514,541
Unamortized Discount/Premium and Deferred Financing Costs		(22,370)		(29,777)
Indebtedness		$ 509,938		$ 484,764
Weighted-Average Interest Rate		4.80%		5.10%
Non-recourse indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 1,455,953		$ 1,938,026
Unamortized Discount/Premium and Deferred Financing Costs		(14,443)		(23,315)
Indebtedness		$ 1,441,510		$ 1,914,711
Weighted-Average Interest Rate		2.70%		2.10%
7.0% convertible senior notes | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 871	[1]	$ 30,048	[2]
Unamortized Discount/Premium and Deferred Financing Costs		(27)	[1]	(1,180)	[2]
Indebtedness		$ 844	[1]	$ 28,868	[2]
Weighted-Average Interest Rate		7.00%	[1]	7.00%	[2]
Contractual Maturity, month and year		2031-04	[1]	2031-04	[2]
4.0% convertible senior notes | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	[3]	$ 126,098		$ 141,750
Unamortized Discount/Premium and Deferred Financing Costs	[3]	(6,215)		(8,711)
Indebtedness	[3]	$ 119,883		$ 133,039
Weighted-Average Interest Rate	[3]	4.00%		4.00%
Contractual Maturity, month and year	[3]	2033-10		2033-10
7.625% senior notes due 2024 | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 57,287		$ 60,000
Unamortized Discount/Premium and Deferred Financing Costs		(1,747)		(2,048)
Indebtedness		$ 55,540		$ 57,952
Weighted-Average Interest Rate		7.60%		7.60%
Contractual Maturity, month and year		2024-04		2024-04
7.125% Senior Notes due 2019 | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 70,731		$ 71,905
Unamortized Discount/Premium and Deferred Financing Costs		(1,545)		(2,156)
Indebtedness		$ 69,186		$ 69,749
Weighted-Average Interest Rate		7.10%		7.10%
Contractual Maturity, month and year		2019-08		2019-08
Senior Secured Notes | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 64,000		$ 70,000
Unamortized Discount/Premium and Deferred Financing Costs		(4,560)		(6,955)
Indebtedness		$ 59,440		$ 63,045
Weighted-Average Interest Rate		7.00%		7.00%
Senior Secured Notes | Minimum | Recourse Indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year		2017-04		2017-04
Senior Secured Notes | Maximum | Recourse Indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year		2019-04		2019-04
Junior Subordinated Notes, at Fair Value | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	[4]	$ 18,671		$ 18,671
Unamortized Discount/Premium and Deferred Financing Costs	[4]	(7,147)		(8,167)
Indebtedness	[4]	$ 11,524		$ 10,504
Weighted-Average Interest Rate	[4]	4.60%		4.30%
Contractual Maturity, month and year	[4]	2035-03		2035-03
Junior subordinated notes, at amortized cost | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 25,100		$ 25,100
Unamortized Discount/Premium and Deferred Financing Costs		(208)		(216)
Indebtedness		$ 24,892		$ 24,884
Weighted-Average Interest Rate		3.30%		2.70%
Contractual Maturity, month and year		2037-04		2037-04
CMBS Facilities | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 169,550		$ 97,067
Unamortized Discount/Premium and Deferred Financing Costs		(921)		(344)
Indebtedness		$ 168,629		$ 96,723
Weighted-Average Interest Rate		2.80%		2.40%
CMBS Facilities | Minimum | Recourse Indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year		2016-11		2016-07
CMBS Facilities | Maximum | Recourse Indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year		2018-07		2018-01
CDO notes payable, at amortized cost | Non-recourse indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	[6]	$ 728,362	[5]	$ 950,981	[7]
Unamortized Discount/Premium and Deferred Financing Costs	[6]	(9,165)	[5]	(13,412)	[7]
Indebtedness	[6]	$ 719,197	[5]	$ 937,569	[7]
Weighted-Average Interest Rate	[6]	1.40%	[5]	0.90%	[7]
CDO notes payable, at amortized cost | Minimum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year	[6],[7]			2045-06
Contractual Maturity, year	[5],[6]	2045
CDO notes payable, at amortized cost | Maximum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year	[6],[7]			2046-11
Contractual Maturity, year	[5],[6]	2046
Loans payable on real estate | Non-recourse indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance		$ 230,678	[8]	$ 269,790
Unamortized Discount/Premium and Deferred Financing Costs		(858)	[8]	(1,158)
Indebtedness		$ 229,820	[8]	$ 268,632
Weighted-Average Interest Rate		5.80%	[8]	5.60%
Loans payable on real estate | Minimum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year		2016-06	[8]	2016-04
Loans payable on real estate | Maximum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year		2026-04	[8]	2026-04
Other indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	[9]	$ 24,321
Unamortized Discount/Premium and Deferred Financing Costs	[9]	94
Indebtedness	[9]	24,415
CMBS securitizations | Non-recourse indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance		496,913	[10]	$ 717,255	[11]
Unamortized Discount/Premium and Deferred Financing Costs		(4,420)	[10]	(8,745)	[11]
Indebtedness		$ 492,493	[10]	$ 708,510	[11]
Weighted-Average Interest Rate		3.10%	[10]	2.40%	[11]
CMBS securitizations | Minimum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year		2031-01	[10]	2031-05	[11]
CMBS securitizations | Maximum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year		2031-12	[10]	2031-12	[11]

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

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

[3] Our 4.0% convertible senior notes are redeemable at par, at the option of the holder, in October 2018, October 2023, and October 2028.

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

[5] Collateralized by $1,107,924 principal amount of commercial mortgage loans, mezzanine loans, other loans and preferred equity interests, $641,118 of which eliminates in consolidation. 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.

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

[7] Collateralized by $1,388,194 principal amount of commercial mortgage loans, mezzanine loans, other loans and preferred equity interests, $815,745 of which eliminates in consolidation. 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] Certain loans payable on real estate had maturity dates of June 2016. These loans payable on real estate are currently in the process of being refinanced with the lenders.

[9] Represents a 40% interest issued to an unaffiliated third party in a venture to which we contributed the junior notes and equity of a floating rate securitization. We retained a 60% interest in this venture, and, as a result of our controlling financial interest, we consolidated the venture. We received approximately $24,796 of proceeds as a result of issuing this 40% interest, which has an unpaid principal balance of $24,321. This 40% interest has no stated maturity date and does not provide for its mandatory redemption or any required return or interest payment. The venture interests allocate the distributions on such junior notes and equity when made between the parties to the venture.

[10] Collateralized by $618,494 principal amount of commercial mortgage loans and participation 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.

[11] Collateralized by 885,055 principal amount of commercial mortgage loans and participation 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.