Investments in and Advances to Unconsolidated Real Estate Ventures - Condensed Combined Financial Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Combined balance sheet information:
Real estate, net	$ 2,106,670	$ 463,643
Other assets	264,731	134,596
Total assets	2,371,401	598,239
Mortgages payable, net	1,190,202	302,966
Other liabilities	76,415	24,896
Total liabilities	1,266,617	327,862
Noncontrolling interests	0	343
Total equity	1,104,784	270,034
Total liabilities and equity	2,371,401	598,239
Combined income statement information:
Total revenue	135,256	68,118	$ 67,275
Operating income	14,741	19,283	21,173
Net income (loss)	$ (7,593)	$ 5,234	$ 340