Organization, Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Operating Partnership's Equity Interest (Details) - USD ($) $ in Millions	1 Months Ended	6 Months Ended
	Apr. 30, 2018	Jun. 30, 2018
Fund II and Mervyns II
Variable Interest Entity [Line Items]
Operating Partnership Share of Capital		28.33%
Capital called		$ 347.1
Unfunded Commitment		$ 0.0
Equity Interest Held By Operating Partnership		28.33%
Preferred Return		8.00%
Total distributions		$ 146.6
Fund II
Variable Interest Entity [Line Items]
Total distributions	$ 15.0
Fund III
Variable Interest Entity [Line Items]
Operating Partnership Share of Capital		24.54%
Capital called		$ 420.2
Unfunded Commitment		$ 29.8
Equity Interest Held By Operating Partnership		24.54%
Preferred Return		6.00%
Total distributions		$ 551.9
Fund IV
Variable Interest Entity [Line Items]
Operating Partnership Share of Capital		23.12%
Capital called		$ 412.7
Unfunded Commitment		$ 117.3
Equity Interest Held By Operating Partnership		23.12%
Preferred Return		6.00%
Total distributions		$ 136.7
Fund V
Variable Interest Entity [Line Items]
Operating Partnership Share of Capital		20.10%
Capital called		$ 45.8
Unfunded Commitment		$ 474.2
Equity Interest Held By Operating Partnership		20.10%
Preferred Return		6.00%
Total distributions		$ 0.0
Operating Partnership, as General Partner or Managing Member
Variable Interest Entity [Line Items]
Total distributions	$ 4.3