Schedule IV - Mortgage Loans on Real Estate (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Mortgage Loans on Real Estate [Line Items]
Prior Liens	$ 199,374
Face Amount of Loans	4,462,897
Carrying Amount of Loans	4,428,500
Senior Mortgage Loans [Member]
Mortgage Loans on Real Estate [Line Items]
Face Amount of Loans	4,374,532
Carrying Amount of Loans	4,340,586
Senior Mortgage Loans [Member] \| Various / Diversified [Member] \| All Other Mortgage Loans Individually Less Than 3% [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Various / Diversified
Debt instrument variable rate basis	LIBOR
Maximum Maturity Date - earliest	Jun. 10, 2016
Maximum Maturity Date	Sep. 30, 2020
Face Amount of Loans	2,852,148
Carrying Amount of Loans	2,831,478
Senior Mortgage Loans [Member] \| Hotel [Member] \| Borrower A [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Hotel / UK
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	4.00%
Maximum Maturity Date	May 22, 2019
Periodic Payment Terms	I/O
Face Amount of Loans	311,240
Carrying Amount of Loans	307,084
Senior Mortgage Loans [Member] \| Hotel [Member] \| Borrower F [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Hotel / UK
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	3.40%
Maximum Maturity Date	Nov. 20, 2019
Periodic Payment Terms	I/O
Face Amount of Loans	149,395
Carrying Amount of Loans	147,936
Senior Mortgage Loans [Member] \| Hotel [Member] \| Borrower I [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Hotel / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	4.30%
Maximum Maturity Date	Dec. 01, 2017
Periodic Payment Terms	I/O
Face Amount of Loans	133,350
Carrying Amount of Loans	132,987
Senior Mortgage Loans [Member] \| Condo / Northeast [Member] \| Borrower B [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Condo / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	4.50%
Maximum Maturity Date	Nov. 09, 2018
Periodic Payment Terms	I/O
Face Amount of Loans	181,000
Carrying Amount of Loans	179,839
Senior Mortgage Loans [Member] \| Office [Member] \| Borrower C [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / Diversified
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	3.80%
Maximum Maturity Date	Dec. 09, 2019
Periodic Payment Terms	I/O
Face Amount of Loans	163,300
Carrying Amount of Loans	161,770
Senior Mortgage Loans [Member] \| Office [Member] \| Borrower D [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / Midwest
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	3.50%
Maximum Maturity Date	Aug. 09, 2019
Periodic Payment Terms	I/O
Face Amount of Loans	153,879
Carrying Amount of Loans	152,751
Senior Mortgage Loans [Member] \| Office [Member] \| Borrower G [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	4.75%
Maximum Maturity Date	Jan. 09, 2019
Periodic Payment Terms	I/O
Face Amount of Loans	139,809
Carrying Amount of Loans	139,099
Senior Mortgage Loans [Member] \| Office [Member] \| Borrower H [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / Canada
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	5.50%
Maximum Maturity Date	Dec. 09, 2019
Periodic Payment Terms	I/O
Face Amount of Loans	138,644
Carrying Amount of Loans	137,024
Senior Mortgage Loans [Member] \| Other [Member] \| Borrower E [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Other / Diversified
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	4.75%
Maximum Maturity Date	Jan. 07, 2019
Periodic Payment Terms	I/O
Face Amount of Loans	151,767
Carrying Amount of Loans	150,618
Subordinate Loans [Member]
Mortgage Loans on Real Estate [Line Items]
Prior Liens	199,374
Face Amount of Loans	88,365
Carrying Amount of Loans	87,914
Subordinate Loans [Member] \| Condo / Northeast [Member] \| Borrower BB [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Condo / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	12.56%
Maximum Maturity Date	Dec. 13, 2017
Periodic Payment Terms	I/O
Prior Liens	110,388
Face Amount of Loans	33,966
Carrying Amount of Loans	34,081
Subordinate Loans [Member] \| Office [Member] \| Borrower AA [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / Northwest
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	5.66%
Maximum Maturity Date	Apr. 09, 2015
Periodic Payment Terms	I/O
Prior Liens	88,986
Face Amount of Loans	54,399
Carrying Amount of Loans	$ 53,833
Minimum [Member] \| Senior Mortgage Loans [Member] \| Various / Diversified [Member] \| All Other Mortgage Loans Individually Less Than 3% [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	365.00%
Maximum [Member] \| Senior Mortgage Loans [Member] \| Various / Diversified [Member] \| All Other Mortgage Loans Individually Less Than 3% [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	683.00%

Mortgage Loan On Real Estate Final Maturity Date In Range Earliest

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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.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule IV)

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-Number 210

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-SubTopic 310

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- Definition

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

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- Definition

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

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- Definition

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

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule IV)

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule IV)

-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

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-Number 210

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-Article 12

Reference 3: 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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