Fair Value Disclosures (Details) - Fair Value, Inputs, Level 2 [Member] - SPG Units [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Units of Partnership Interest, Amount	590,124	590,124
Partnership Units Received as Part of Consideration in Connection with Sale of Equity Method Investment and Other Assets, Fair Value at Reporting Date	$ 122,600	$ 114,700
Partnership Units Received as Part of Consideration in Connection with Sale of Equity Method Investment and Other Assets, Book Value	$ 77,700	$ 77,700