Variable Interest Entities - Summary of Investments in Unconsolidated Real Estate Funds and Maximum Risk of Loss from Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Investments in unconsolidated real estate funds	$ 7,253	$ 28,173
Investment [Member]
Variable Interest Entity [Line Items]
Investments in unconsolidated real estate funds	7,253	28,173
Asset Management Fees and Other Receivables [Member]
Variable Interest Entity [Line Items]
Investments in unconsolidated real estate funds	597	1,680
Maximum Risk of Loss [Member]
Variable Interest Entity [Line Items]
Investments in unconsolidated real estate funds	$ 7,850	$ 29,853