Schedule IV - Mortgage Loans on Real Estate (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Mortgage Loans on Real Estate [Line Items]
Prior Liens	$ 1,029,516
Face Amount of Loans	8,727,218	$ 9,108,361
Carrying Amount of Loans	$ 8,692,978
Senior Mortgage Loans in Excess of 3% of the Carrying Amount of Total Loans [Member] \| Borrower A [Member] \| Hotel [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Hotel / U.K.
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	4.20%
Maximum Maturity Date	2019
Periodic Payment Terms	I/O
Face Amount of Loans	$ 419,560
Carrying Amount of Loans	$ 416,233
Senior Mortgage Loans in Excess of 3% of the Carrying Amount of Total Loans [Member] \| Borrower B [Member] \| Office [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	3.45%
Maximum Maturity Date	2020
Periodic Payment Terms	I/O
Face Amount of Loans	$ 294,500
Carrying Amount of Loans	$ 293,110
Senior Mortgage Loans in Excess of 3% of the Carrying Amount of Total Loans [Member] \| Borrower C [Member] \| Office [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	3.50%
Maximum Maturity Date	2020
Periodic Payment Terms	I/O
Face Amount of Loans	$ 284,012
Carrying Amount of Loans	$ 282,818
Senior Mortgage Loans in Excess of 3% of the Carrying Amount of Total Loans [Member] \| Borrower D [Member] \| Hotel [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Hotel / Canada
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	4.34%
Maximum Maturity Date	2020
Periodic Payment Terms	I/O & P/I
Face Amount of Loans	$ 259,143
Carrying Amount of Loans	262,186
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member]
Mortgage Loans on Real Estate [Line Items]
Face Amount of Loans	7,232,335
Carrying Amount of Loans	$ 7,202,642
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Hotel [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Hotel / Diversified
Debt instrument variable rate basis	LIBOR
Periodic Payment Terms	I/O & P/I
Face Amount of Loans	$ 1,207,130
Carrying Amount of Loans	$ 1,203,255
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Hotel [Member] \| Minimum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	3.65%
Maximum Maturity Date	2017
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Hotel [Member] \| Maximum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	4.60%
Maximum Maturity Date	2021
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Office [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / Diversified
Debt instrument variable rate basis	LIBOR
Periodic Payment Terms	I/O & P/I
Face Amount of Loans	$ 4,376,823
Carrying Amount of Loans	$ 4,353,624
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Office [Member] \| Minimum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	2.30%
Maximum Maturity Date	2017
Fixed Interest Payment Rates	4.50%
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Office [Member] \| Maximum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	5.75%
Maximum Maturity Date	2022
Fixed Interest Payment Rates	5.29%
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Retail [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Retail / Diversified
Debt instrument variable rate basis	LIBOR
Periodic Payment Terms	I/O & P/I
Face Amount of Loans	$ 621,548
Carrying Amount of Loans	$ 620,303
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Retail [Member] \| Minimum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	3.10%
Maximum Maturity Date	2017
Fixed Interest Payment Rates	5.14%
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Retail [Member] \| Maximum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	4.50%
Maximum Maturity Date	2021
Fixed Interest Payment Rates	5.38%
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Multifamily [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Multifamily / Diversified
Debt instrument variable rate basis	LIBOR
Periodic Payment Terms	I/O & P/I
Face Amount of Loans	$ 439,421
Carrying Amount of Loans	$ 437,036
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Multifamily [Member] \| Minimum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	3.40%
Maximum Maturity Date	2018
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Multifamily [Member] \| Maximum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	4.65%
Maximum Maturity Date	2022
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| MHC [Member]
Mortgage Loans on Real Estate [Line Items]
Location	MHC / Diversified
Debt instrument variable rate basis	LIBOR
Periodic Payment Terms	I/O & P/I
Face Amount of Loans	$ 296,252
Carrying Amount of Loans	$ 296,290
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| MHC [Member] \| Minimum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	3.20%
Maximum Maturity Date	2017
Fixed Interest Payment Rates	4.67%
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| MHC [Member] \| Maximum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	4.40%
Maximum Maturity Date	2020
Fixed Interest Payment Rates	5.97%
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Condo / Northeast [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Condo / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	3.75%
Periodic Payment Terms	P/I
Face Amount of Loans	$ 18,677
Carrying Amount of Loans	$ 18,677
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Condo / Northeast [Member] \| Maximum [Member]
Mortgage Loans on Real Estate [Line Items]
Maximum Maturity Date	2019
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Other [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Other / Diversified
Debt instrument variable rate basis	LIBOR
Maximum Maturity Date	2017
Periodic Payment Terms	I/O & P/I
Face Amount of Loans	$ 272,484
Carrying Amount of Loans	$ 273,457
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Other [Member] \| Minimum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	3.30%
Maximum Maturity Date	2017
Fixed Interest Payment Rates	4.63%
Senior Mortgage Loans Less Than 3% of the Carrying Amount of Total Loans [Member] \| Other [Member] \| Maximum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	4.00%
Maximum Maturity Date	2021
Fixed Interest Payment Rates	5.17%
Senior Mortgage Loans [Member]
Mortgage Loans on Real Estate [Line Items]
Face Amount of Loans	$ 8,489,550
Carrying Amount of Loans	8,456,989
Subordinate Loans [Member]
Mortgage Loans on Real Estate [Line Items]
Prior Liens	1,029,516
Face Amount of Loans	237,668
Carrying Amount of Loans	$ 235,989
Subordinate Loans [Member] \| Various / Diversified [Member]
Mortgage Loans on Real Estate [Line Items]
Debt instrument variable rate basis	LIBOR
Fixed Interest Payment Rates	12.22%
Periodic Payment Terms	I/O & P/I
Prior Liens	$ 1,029,516
Face Amount of Loans	237,668
Carrying Amount of Loans	$ 235,989
Subordinate Loans [Member] \| Various / Diversified [Member] \| Minimum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	10.75%
Maximum Maturity Date	2017
Subordinate Loans [Member] \| Various / Diversified [Member] \| Maximum [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	12.83%
Maximum Maturity Date	2022

Stated maturity date of the mortgage loan receivable on real estate, in CCYY format.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

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Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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- Definition

The carrying amount of the outstanding balance due under the mortgage loan.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 10
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- Definition

Amount of the contractual principal due at the origination of the mortgage loan (face amount).

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Identifies the site (such as country, region, state, county or municipality) of the property or properties under mortgage.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

Description of the contractual payment terms of the loan receivable including whether principal and interest is payable at a level or varying amount over the life of the loan, the amount of any balloon payment required at maturity, and any prepayment penalties.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount of prior lien on the real estate that secures the mortgage loan.

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