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, 2019
Fund II and Mervyns II
Variable Interest Entity [Line Items]
Operating Partnership Share of Capital		28.33%
Capital Called		$ 347.1
Unfunded Commitment		$ 15.0
Equity interest held by Operating Partnership		28.33%
Preferred Return		8.00%
Total Distributions		$ 146.6
Fund III
Variable Interest Entity [Line Items]
Operating Partnership Share of Capital		24.54%
Capital Called		$ 426.3
Unfunded Commitment		$ 23.7
Equity interest held by Operating Partnership		24.54%
Preferred Return		6.00%
Total Distributions		$ 554.8
Fund IV
Variable Interest Entity [Line Items]
Operating Partnership Share of Capital		23.12%
Capital Called		$ 425.4
Unfunded Commitment		$ 104.6
Equity interest held by Operating Partnership		23.12%
Preferred Return		6.00%
Total Distributions		$ 147.4
Fund V
Variable Interest Entity [Line Items]
Operating Partnership Share of Capital		20.10%
Capital Called		$ 118.3
Unfunded Commitment		$ 401.7
Equity interest held by Operating Partnership		20.10%
Preferred Return		6.00%
Total Distributions		$ 2.0
Fund II
Variable Interest Entity [Line Items]
Total Distributions	$ 15.0
Operating Partnership, as General Partner or Managing Member
Variable Interest Entity [Line Items]
Total Distributions	$ 4.3