Loans Receivable - Schedule of fair values and risk ratings (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	28
Fair Value | $	$ 1,631.0	$ 1,572.1
% of Fair Value	100.00%	100.00%
Related Party
Financing Receivable, Credit Quality Indicator [Line Items]
Number of loans collateralized by equity interests in real estate investments	2
BBB
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	10
Fair Value | $	$ 558.6
BBB | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	34.20%
BB
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	8
Fair Value | $	$ 452.7
BB | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	27.80%
B
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	7
Fair Value | $	$ 473.3
B | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	29.00%
D
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	1
Fair Value | $	$ 77.9
D | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	4.80%
NR
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	2
Fair Value | $	$ 68.5
NR | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	4.20%