Preferred Equity and Mezzanine Loan Investments (Details) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan
Variable Interest Entity [Line Items]
Total	$ 154,006	$ 138,920
New York
Variable Interest Entity [Line Items]
Geographic concentration, percent	22.00%	24.10%
Texas
Variable Interest Entity [Line Items]
Geographic concentration, percent	21.70%	24.30%
Florida
Variable Interest Entity [Line Items]
Geographic concentration, percent	15.30%	3.90%
Virginia
Variable Interest Entity [Line Items]
Geographic concentration, percent	9.80%	10.80%
Alabama
Variable Interest Entity [Line Items]
Geographic concentration, percent	6.50%	7.10%
South Carolina
Variable Interest Entity [Line Items]
Geographic concentration, percent	6.40%	7.00%
Preferred equity and mezzanine loan investments
Variable Interest Entity [Line Items]
Investment amount	$ 155,604	$ 140,560
Deferred loan fees, net	(1,598)	(1,640)
Total	$ 154,006	$ 138,920
Number of delinquent loans \| loan	0	0

The aggregate number of delinquent loans.

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
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-Section 50
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

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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

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph a
-URI http://asc.fasb.org/extlink&oid=77990344&loc=d3e5728-111685

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- Definition

Net carrying amount of the assets and liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), when the reporting entity is not the VIE's primary beneficiary.

+ References

No definition available.

+ Details

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- Definition

Carrying amount of the liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

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