Variable Interest Entities ("VIE") (Details) - Jun. 30, 2015 - USD ($) $ in Millions	Total
Variable Interest Entity, Primary Beneficiary [Member] | Consolidated Ground-Up Development Projects [Member]
Variable Interest Entity [Line Items]
Total assets of ground-up development VIE	$ 77.8
Total liabilities of this ground-up development VIE	0.3
Costs to be funded for ground-up development VIE	32.8
Variable Interest Entity, Not Primary Beneficiary [Member] | Unconsolidated Ground Up Development [Member]
Variable Interest Entity [Line Items]
Investment in VIE	38.3
Maximum exposure to loss with VIE	38.3
Variable Interest Entity, Not Primary Beneficiary [Member] | Unconsolidated Redevelopment Investment [Member]
Variable Interest Entity [Line Items]
Costs to be funded for ground-up development VIE	(7.4)
Maximum exposure to loss with VIE	$ 7.4