Summary of Total Recourse and Non-Recourse Indebtedness (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Debt Instrument [Line Items]
Unpaid Principal Balance	$ 3,043,419		$ 2,592,414
Carrying Amount	2,613,317		2,086,401
Weighted- Average Interest Rate	1.90%		1.40%
Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	515,663	[1]	251,715	[2]
Carrying Amount	501,273	[1]	235,011	[2]
Weighted- Average Interest Rate	4.40%	[1]	3.80%	[2]
Non-recourse indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	2,527,756		2,340,699
Carrying Amount	2,112,044		1,851,390
Weighted- Average Interest Rate	1.40%		1.10%
7.0% convertible senior notes | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	34,066	[3]	34,066	[3]
Carrying Amount	33,297	[3]	32,938	[3]
Weighted- Average Interest Rate	7.00%	[3]	7.00%	[3]
Contractual Maturity, month and year	2031-04	[3]	2031-04	[3]
4.0% convertible senior notes | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	141,750	[4]	125,000	[4]
Carrying Amount	133,752	[4]	116,184	[4]
Weighted- Average Interest Rate	4.00%	[4]	4.00%	[4]
Contractual Maturity, month and year	2033-10	[4]	2033-10	[4]
CMBS Facilities
Debt Instrument [Line Items]
Carrying Amount	1,573,559		1,662,537
CMBS Facilities | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	159,171		37,746
Carrying Amount	159,171		37,749
Weighted- Average Interest Rate	2.40%		2.70%
CMBS Facilities | Minimum | Recourse Indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year	2014-11		2014-11
CMBS Facilities | Maximum | Recourse Indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year	2016-07		2015-10
Secured credit facilities | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	5,000		11,129
Carrying Amount	5,000		11,129
Weighted- Average Interest Rate	2.70%		3.20%
Contractual Maturity, month and year	2016-10
Secured credit facilities | Minimum | Recourse Indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year			2016-10
Secured credit facilities | Maximum | Recourse Indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year			2016-12
Junior Subordinated Notes, at Fair Value | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	18,671	[5]	18,671	[5]
Carrying Amount	13,048	[5]	11,911	[5]
Weighted- Average Interest Rate	0.50%	[5]	0.50%	[5]
Contractual Maturity, month and year	2035-03	[5]	2035-03	[5]
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	2.70%		2.70%
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	1,086,038	[6],[7]	1,204,117	[6],[8]
Carrying Amount	1,084,289	[6],[7]	1,202,772	[6],[8]
Weighted- Average Interest Rate	0.60%	[6],[7]	0.60%	[6],[8]
CDO notes payable, at amortized cost | Minimum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, year	2045	[6],[7]	2045	[6],[8]
CDO notes payable, at amortized cost | Maximum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, year	2046	[6],[7]	2046	[6],[8]
CDO notes payable, at fair value | Non-recourse indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	846,941	[5],[6],[9]	865,199	[10],[5],[6]
Carrying Amount	431,142	[5],[6],[9]	377,235	[10],[5],[6]
Weighted- Average Interest Rate	1.00%	[5],[6],[9]	0.90%	[10],[5],[6]
CDO notes payable, at fair value | Minimum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, year	2037	[5],[6],[9]	2037	[10],[5],[6]
CDO notes payable, at fair value | Maximum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, year	2038	[5],[6],[9]	2038	[10],[5],[6]
Loans payable on real estate | Non-recourse indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	379,259	[11]	171,244	[12]
Carrying Amount	381,095	[11]	171,244	[12]
Weighted- Average Interest Rate	4.70%	[11]	5.30%	[12]
Loans payable on real estate | Minimum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year	2015-09	[11]	2015-09	[12]
Loans payable on real estate | Maximum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year	2024-08	[11]	2023-12	[12]
7.625% senior notes due 2024 | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	60,000
Carrying Amount	60,000
Weighted- Average Interest Rate	7.60%
Contractual Maturity, month and year	2024-04
7.125% Senior Notes due 2019 | Recourse Indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	71,905
Carrying Amount	71,905
Weighted- Average Interest Rate	7.10%
Contractual Maturity, month and year	2019-08
CMBS securitizations
Debt Instrument [Line Items]
Carrying Amount	289,470		131,843
CMBS securitizations | Non-recourse indebtedness
Debt Instrument [Line Items]
Unpaid Principal Balance	215,518	[13]	100,139	[14]
Carrying Amount	$ 215,518	[13]	$ 100,139	[14]
Weighted- Average Interest Rate	1.90%	[13]	2.10%	[14]
Contractual Maturity, month and year			2029-01	[14]
CMBS securitizations | Minimum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year	2029-01	[13]
CMBS securitizations | Maximum | Non-recourse indebtedness
Debt Instrument [Line Items]
Contractual Maturity, month and year	3031-05	[13]

[1] Excludes senior secured notes issued by us with an aggregate principal amount equal to $80,000 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 $86,000 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] Our 4.0% convertible senior notes are redeemable at par, at the option of the holder, in October 2018, October 2023, and October 2028.

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

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

[7] Collateralized by $1,573,559 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 $1,662,537 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.

[9] Collateralized by $959,310 principal amount of investments in securities and security-related receivables and loans, before fair value adjustments. The fair value of these investments as of September 30, 2014 was $731,911. 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.

[10] Collateralized by $989,781 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, 2013 was $746,939. 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] Includes $246,997 of unpaid principal balance with a carrying amount of $248,833 of mortgage indebtedness that encumbers properties owned by IRT. The weighted-average interest rate is 3.7% and has a range of maturity dates from April 2016 to August 2024.

[12] Includes $100,803 of unpaid principal balance and carrying amount of mortgage indebtedness that encumbers properties owned by IRT. The weighted-average interest rate is 3.8% and has a range of maturity dates from January 2019 to November 2022.

[13] Excludes the FL1 junior notes and the FL2 junior notes purchased by us which are eliminated in consolidation. Collateralized by $289,470 principal amount of commercial mortgages 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.

[14] Excludes the FL1 junior notes purchased by us which are eliminated in consolidation. Collateralized by $131,843 principal amount of commercial mortgages 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.