Aggregate Principal Amounts Due on Mortgage Notes Payable by Unconsolidated LLCs, Accounted Under Equity Method (Detail) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2018	Dec. 31, 2017
Schedule Of Equity Method Investments [Line Items]
Mortgage Loan Balance		$ 27,404	$ 27,839
Equity Method Investments
Schedule Of Equity Method Investments [Line Items]
Mortgage Loan Balance	[1]	27,404	27,839
Equity Method Investments | FTX MOB Phase II
Schedule Of Equity Method Investments [Line Items]
Mortgage Loan Balance	[1]	$ 5,102	5,202
Maturity Date		2020-10
Equity Method Investments | Grayson Properties
Schedule Of Equity Method Investments [Line Items]
Mortgage Loan Balance	[1]	$ 13,996	14,191
Maturity Date		2021-09
Equity Method Investments | Brunswick Associates
Schedule Of Equity Method Investments [Line Items]
Mortgage Loan Balance	[1]	$ 8,306	$ 8,446
Maturity Date		2024-12

[1] All mortgage loans require monthly principal payments through maturity and include a balloon principal payment upon maturity