Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Principles of Consolidation
Commercial real estate properties	$ 7,906,006	$ 10,478,638
Mortgages and other loans payable, net	2,837,282	4,073,830
Assets held for sale	338,354	0
Liabilities related to assets held for sale	4,074	0
Consolidated VIEs
Principles of Consolidation
Mortgages and other loans payable, net	$ 628,900	$ 621,800

Amount classified as assets attributable to disposal group held for sale or disposed of.

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