Noncontrolling Interests - Variable interest entity (Details) - Variable Interest Entities, Primary Beneficiary, Aggregated Disclosure - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Variable interest entity
Net real estate	$ 2,955,112	$ 2,936,397
Total assets	3,352,666	3,342,443
Total debt	198,670	210,384
Total liabilities	$ 312,315	$ 313,295