Variable Interest Entities ("VIEs") - Summary of Investments in Unconsolidated Real Estate Funds and Maximum Risk of Loss from Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Investments in unconsolidated real estate funds	$ 8,163	$ 10,352
Investment [Member]
Variable Interest Entity [Line Items]
Investments in unconsolidated real estate funds	8,163	10,352
Asset Management Fees and Other Receivables [Member]
Variable Interest Entity [Line Items]
Investments in unconsolidated real estate funds	11,156	722
Maximum Risk of Loss [Member]
Variable Interest Entity [Line Items]
Investments in unconsolidated real estate funds	$ 19,319	$ 11,074