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Residential Mortgage Loans, At Fair Value - Concentration of Risk (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Florida
Concentration Risk [Line Items]
Geographic concentration, percent	15.30%	3.90%
Geographic Concentration Risk | Residential mortgage loans, at fair value | California
Concentration Risk [Line Items]
Geographic concentration, percent	36.40%	35.90%
Geographic Concentration Risk | Residential mortgage loans, at fair value | New Jersey
Concentration Risk [Line Items]
Geographic concentration, percent	7.90%	7.70%
Geographic Concentration Risk | Residential mortgage loans, at fair value | Florida
Concentration Risk [Line Items]
Geographic concentration, percent	6.60%	6.60%

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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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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
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-Publisher FASB
-Name Accounting Standards Codification
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