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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Equity Investments - Liquidating Trust's Nominal Ownership Percentages in its Equity Investments (Parenthetical) (Detail) - New Valley/Witkoff [Member] - 701 Seventh WRT Investor LLC [Member]	Dec. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Effective ownership interest of trust in underlying property	60.08%
Winthrop Realty Trust [Member]
Schedule of Equity Method Investments [Line Items]
Effective ownership interest of trust in underlying property		60.72%