Loans and Preferred Equity Held for Investment, net - Summary of Loans and Preferred Equity Held for Investment by Year of Origination and Credit Quality Risk Ranking (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 21,069
2019	1,316,314
2018	756,251
2017	45,780
2016	0
Prior	4,524
Total	2,143,938	$ 2,848,956
Senior loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	19,500
2019	1,206,859
2018	682,417
2017	33,660
2016	0
Prior	0
Total	1,942,436
Senior loans | Risk Ranking 3
Financing Receivable, Credit Quality Indicator [Line Items]
2020	19,500
2019	371,654
2018	279,223
2017	33,660
2016	0
Prior	0
Total	704,037
Senior loans | Risk Ranking 4
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	835,205
2018	403,194
2017	0
2016	0
Prior	0
Total	1,238,399
Mezzanine loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	95,848
2018	55,484
2017	12,120
2016	0
Prior	4,524
Total	167,976
Mezzanine loans | Risk Ranking 4
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	95,848
2018	55,484
2017	12,120
2016	0
Prior	4,524
Total	167,976
Preferred equity interests and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,569
2019	13,607
2018	18,350
2017	0
2016	0
Prior	0
Total	33,526
Preferred equity interests and other | Risk Ranking 4
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,569
2019	0
2018	18,350
2017	0
2016	0
Prior	0
Total	19,919
Preferred equity interests and other | Risk Ranking 5
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	13,607
2018	0
2017	0
2016	0
Prior	0
Total	$ 13,607