Fair Value of Financial Instruments - Summary of Quantitative Information About Significant Unobservable Inputs Related to Level 3 Fair Value Measurements (Detail) - Significant Unobservable Inputs (Level 3) $ in Thousands	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Significant Unobservable Inputs, Discount Rate | Fair Value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Rreef America REIT II	$ 2,237	$ 2,150
Significant Unobservable Inputs, Discount Rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant unobservable inputs	0.0525	0.0550
Significant Unobservable Inputs, Discount Rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant unobservable inputs	0.0875	0.0900
Significant Unobservable Inputs, Discount Rate | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant unobservable inputs	0.0648	0.0661
Significant Unobservable Inputs, Terminal Capitalization Rate | Minimum | Fair Value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant unobservable inputs	0.0425	0.0400
Significant Unobservable Inputs, Terminal Capitalization Rate | Maximum | Fair Value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant unobservable inputs	0.0814	0.0825
Significant Unobservable Inputs, Terminal Capitalization Rate | Weighted Average | Fair Value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Significant unobservable inputs	0.0543	0.0562