Mortgage Payable and Other Secured Financing - Summary of Partnerships' Mortgage Payable and Other Secured Financing, Net of Deferred Financing Costs (Parenthetical) (Details)	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Wall Street Journal Prime Rate [Member] \| Maximum [Member]
Mortgage Loans on Real Estate [Line Items]
Variable Based Rate	5.00%	5.00%

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.

No definition available.

Name:	srt_MortgageLoansOnRealEstateLineItems
Namespace Prefix:	srt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration