Organization, Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Operating Partnership's Equity Interest (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($)
Fund I and Mervyns I [Member]
Variable Interest Entity [Line Items]
Operating partnership share of capital	22.22%
Fund Size	$ 90.0
Capital called	86.6
Unfunded Commitment	$ 0.0
Equity Interest Held By Operating Partnership (b)	37.78%
Preferred Return	9.00%
Total distributions	$ 194.5
Fund II and Mervyns II [Member]
Variable Interest Entity [Line Items]
Operating partnership share of capital	28.33%
Fund Size	$ 300.0
Capital called	347.1
Unfunded Commitment	$ 0.0
Equity Interest Held By Operating Partnership (b)	28.33%
Preferred Return	8.00%
Total distributions	$ 131.6
Fund III [Member]
Variable Interest Entity [Line Items]
Operating partnership share of capital	24.54%
Fund Size	$ 502.5
Capital called	396.7
Unfunded Commitment	$ 53.3
Equity Interest Held By Operating Partnership (b)	39.63%
Preferred Return	6.00%
Total distributions	$ 551.0
Fund IV [Member]
Variable Interest Entity [Line Items]
Operating partnership share of capital	23.12%
Fund Size	$ 540.6
Capital called	390.7
Unfunded Commitment	$ 139.3
Equity Interest Held By Operating Partnership (b)	23.12%
Preferred Return	6.00%
Total distributions	$ 101.9
Fund V [Member]
Variable Interest Entity [Line Items]
Operating partnership share of capital	20.10%
Fund Size	$ 520.0
Capital called	0.0
Unfunded Commitment	$ 520.0
Equity Interest Held By Operating Partnership (b)	20.10%
Preferred Return	6.00%
Total distributions	$ 0.0