Mortgage Payable and Other Secured Financing - Additional Information (Details) - Residences at DeCordova and Weatherford [Member] - Mortgages payable [Member]	12 Months Ended
Dec. 31, 2017 USD ($)
Mortgage Loans on Real Estate [Line Items]
Line of credit, commitment fee	$ 0
Debt instrument, extended for additional maturity period	2 years

Amount of the fee for available but unused credit capacity under the credit facility.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_LineOfCreditFacilityCommitmentFeeAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration