Investments in Unconsolidated Real Estate Funds - Schedule of Income from Unconsolidated Real Estate Funds Investment, Excluding Fund X (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Net realized losses		$ (126)
Net unrealized (losses) gains	$ (560)	(663)	$ (1,706)
Unconsolidated Real Estate Funds [Member]
Investment Holdings [Line Items]
Investment income	33,814	29,013	20,484
Investment expenses	10,587	7,086	7,466
Net investment income	23,227	21,927	13,018
Net realized losses		(72,134)
Previously recorded unrealized losses		35,682
Net unrealized (losses) gains	(4,656)	(6,266)	14,275
Income (loss) from real estate fund investments	$ 18,571	$ (20,791)	$ 27,293