Summary of Significant Accounting Policies - Variable Interest Entities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Real estate, net	$ 3,309,900	$ 3,028,326
Total assets	3,553,020	3,441,467
Mortgages and notes payable, net	689,810	738,047
Total liabilities	2,212,185	2,028,976
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Real estate, net	682,587	778,265
Total assets	766,025	899,801
Mortgages and notes payable, net	212,792	364,099
Total liabilities	$ 226,331	$ 395,332