Real Estate Securities - Available for Sale Securities by Collateral Type (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Available-for-sale	$ 129,243	$ 239,334
Mezzanine
Investment Holdings [Line Items]
Available-for-sale	0	13,687
Senior IO Securities
Investment Holdings [Line Items]
Available-for-sale	0	25,792
Subordinate Securities
Investment Holdings [Line Items]
Available-for-sale	129,243	199,855
Subordinate Securities | Subordinate
Investment Holdings [Line Items]
Available-for-sale	129,243	199,855
Subordinate Securities | Mezzanine
Investment Holdings [Line Items]
Available-for-sale	0	13,687
Senior IO Securities
Investment Holdings [Line Items]
Available-for-sale	$ 0	$ 25,792