Commitments and Contingencies Springfield Town Center (Details) (Springfield Town Center [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 02, 2014
Springfield Town Center [Member]
Property, Plant and Equipment [Line Items]
Long-term Purchase Commitment, Amount	$ 465.0
Contribution Agreement Operating Partnership Shares Value		125.0
Letters of Credit Outstanding, Amount	46.5
Project Costs And Other Expenses	$ 1.4