Noncontrolling Interests - Variable interest entity (Details) - Variable Interest Entities, Primary Beneficiary, Aggregated Disclosure - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Variable interest entity
Net real estate	$ 2,933,150	$ 2,936,397
Total assets	3,303,585	3,342,443
Total debt	197,960	210,384
Total liabilities	$ 328,573	$ 313,295