Investments in Unconsolidated Real Estate Funds - Schedule of Financial Information of Unconsolidated Real Estate Funds, Excluding Fund X (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investment Holdings [Line Items]
Other assets	$ 91,552	$ 81,596
Total assets	1,426,199	1,404,134
Other liabilities	22,310	14,196
Total liabilities	910,192	901,098
Equity	516,007	503,036
Total liabilities and equity	1,426,199	1,404,134
Unconsolidated Real Estate Funds [Member]
Investment Holdings [Line Items]
Real estate investments	645,013	405,931
Cash and cash equivalents	10,791	5,076
Other assets	10	74
Total assets	655,814	411,081
Other liabilities	1,483	1,308
Total liabilities	1,483	1,308
Equity	654,331	409,773
Total liabilities and equity	$ 655,814	$ 411,081