Investments in Partially Owned Entities (510 West 22nd Street) (Details) - Jun. 24, 2015 - New York 510 West 22nd Street [Member] - Entity [Domain] - Office Building [Member] - Segment Breakdown [Domain] ft² in Thousands, $ in Thousands	USD ($) ft²
Schedule Of Equity Method Investments [Line Items]
Equity method ownership percentage	55.00%
Square Footage Of Real Estate Property	173
Estimated Development Cost | $	$ 225,000
Estimated Project Start Date	third quarter of 2015
Estimated Project Completion Date	2017