Real Estate Securities - Trading Securities by Collateral Type (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Real estate securities	$ 144,162	$ 860,540
Senior IO Securities
Investment Holdings [Line Items]
Real estate securities	28,091	150,067
Subordinate Securities \| Mezzanine
Investment Holdings [Line Items]
Real estate securities	3,651	538,489
Subordinate Securities \| Subordinate
Investment Holdings [Line Items]
Real estate securities	$ 112,420	$ 171,984

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Name:	us-gaap_TradingSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant