New Accounting Pronouncements (Details) - shares	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Management Leasing and Development Revenue as a Percentage of Total Revenue	less than 10%
SPG Units [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available for Sale Securities Held	250,000
Fair Value, Inputs, Level 2 [Member] | SPG Units [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Units of Partnership Interest, Amount	340,124	340,124