THE FREMF TRUSTS - Geographic Concentrations (Details) - FREMF Trusts	12 Months Ended
Dec. 31, 2017
New York
Concentration Risk [Line Items]
Concentration risk (as a percentage)	16.50%
Texas
Concentration Risk [Line Items]
Concentration risk (as a percentage)	14.20%
Washington
Concentration Risk [Line Items]
Concentration risk (as a percentage)	8.70%
Colorado
Concentration Risk [Line Items]
Concentration risk (as a percentage)	7.80%
Georgia
Concentration Risk [Line Items]
Concentration risk (as a percentage)	5.70%

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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