Unconsolidated Investments - Cash Distributions by Investment Type and Location (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Schedule of Equity Method Investments [Line Items]
Operating	$ 57.3
Investing	69.0	$ 35.2
Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	15.0
Investing	8.6
Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	26.6
Investing	16.1
Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	15.7
Investing	44.3
Western U.S. [Member]
Schedule of Equity Method Investments [Line Items]
Operating	55.0
Investing	69.0
Western U.S. [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	15.0
Investing	8.6
Western U.S. [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	24.3
Investing	16.1
Western U.S. [Member] | Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	15.7
Investing	44.3
United Kingdom [Member]
Schedule of Equity Method Investments [Line Items]
Operating	2.3
Investing	0.0
United Kingdom [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.0
Investing	0.0
United Kingdom [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	2.3
Investing	0.0
United Kingdom [Member] | Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.0
Investing	$ 0.0