Aggregate Principal Amounts Due on Mortgage Notes Payable by Unconsolidated LLCs, Accounted Under Equity Method (Parenthetical) (Detail)	Dec. 31, 2017
5.00% Fixed Rate Mortgage Loan | FTX MOB Phase II
Schedule Of Equity Method Investments [Line Items]
Loan interest rate fixed percentage	5.00%
5.034% Fixed Rate Mortgage Loan | Grayson Properties
Schedule Of Equity Method Investments [Line Items]
Loan interest rate fixed percentage	5.034%
3.64% Fixed Rate Mortgage Loan | Brunswick Associates
Schedule Of Equity Method Investments [Line Items]
Loan interest rate fixed percentage	3.64%