Commitments and Contingencies Contractual Obligations (Details) - Construction in Progress $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Other Commitments [Line Items]
Unaccrued contractual obligation and other commitments	$ 150.6
Fashion District Philadelphia | Macerich | Corporate Joint Venture
Other Commitments [Line Items]
Unaccrued contractual obligation and other commitments	$ 300.0
Contractual obligation, period after commencement	48 months