Mortgage Loans on Real Estate (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Mortgage Loans On Real Estate [Line Items]
Prior Liens	$ 1,017,694
Face Amount of Mortgages	402,174
Carrying Amount of Mortgages	297,451
Principal Amount of Loans Subject to Delinquent Principal or Interest	0
Mezzanine Loans [Member] \| Retail [Member]
Mortgage Loans On Real Estate [Line Items]
Prior Liens	64,500
Face Amount of Mortgages	19,540
Carrying Amount of Mortgages	19,675
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Mezzanine Loans [Member] \| Retail [Member] \| Borrower A [Member]
Mortgage Loans On Real Estate [Line Items]
Interest Rate	9.00%
Final Maturity Date	2023-06
Periodic Payment Terms	I
Prior Liens	$ 20,500
Face Amount of Mortgages	7,500
Carrying Amount of Mortgages	7,541
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Mezzanine Loans [Member] \| Retail [Member] \| Borrower B [Member]
Mortgage Loans On Real Estate [Line Items]
Interest Rate	9.00%
Final Maturity Date	2019-06
Periodic Payment Terms	I
Prior Liens	$ 44,000
Face Amount of Mortgages	12,040
Carrying Amount of Mortgages	12,134
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Investments in and Advances to Joint Ventures [Member] \| Borrower C [Member]
Mortgage Loans On Real Estate [Line Items]
Interest Rate	8.50%
Final Maturity Date	2021-10
Periodic Payment Terms	QI
Prior Liens	$ 759,894
Face Amount of Mortgages	300,000
Carrying Amount of Mortgages	220,656
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0
Investments in and Advances to Joint Ventures [Member] \| Borrower D [Member]
Mortgage Loans On Real Estate [Line Items]
Interest Rate	8.50%
Final Maturity Date	2022-12
Periodic Payment Terms	QI
Prior Liens	$ 193,300
Face Amount of Mortgages	82,634
Carrying Amount of Mortgages	57,120
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0

Mortgage loans on real estate final maturity date on demand.

No definition available.

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- Definition

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

+ 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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29)
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29)
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

Reference 2: 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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- Definition

The stated interest rate on the mortgage loan receivable or the weighted average interest rate on a group of loans.

+ References

+ Details

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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.

+ References

No definition available.

+ Details

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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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29.5)
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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- Definition

Amount of principal due on loans that have been delinquent, which may exclude loans having interest delinquent for three months or less, as of the balance sheet date.

+ 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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29.10(a))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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- Definition

Amount of prior lien on the real estate that secures the mortgage loan.

+ References

+ Details

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