Commercial Loans - Narrative (Details) $ in Thousands	1 Months Ended			3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018	Nov. 30, 2015 USD ($)	Mar. 31, 2020 USD ($) entity	Jun. 30, 2019	Dec. 31, 2019 USD ($)
Variable Interest Entity [Line Items]
Variable interest entity, number of entity | entity				2
Total assets				$ 3,203,583		$ 5,160,971
Securitized commercial loans, at fair value				477,131		909,040
Repurchased borrowings				47,500
Securitized commercial loans
Variable Interest Entity [Line Items]
LTV rate					65.50%
COVID response, borrowers requesting forbearance, principal balance				30,000
CMSC Trust
Variable Interest Entity [Line Items]
Securitized commercial loans, at fair value				23,900
Trust certificates issued				23,900
CMSC Trust | Securitized commercial loans
Variable Interest Entity [Line Items]
Amount acquired, eliminated in consolidation			$ 14,000
Variable interest entity, fair value				13,300
London Interbank Offered Rate (LIBOR) | RETL Trust
Variable Interest Entity [Line Items]
Debt instrument, basis spread on variable rate		2.30%
CMSC Trust
Variable Interest Entity [Line Items]
Principal balance				23,943		24,048
Financing Receivables Gross Unrealized Loss Accumulated In Investments				147		0
RETL Trust
Variable Interest Entity [Line Items]
Principal balance				519,735		674,331
Financing Receivables Gross Unrealized Loss Accumulated In Investments				67,589		0
RETL Trust | Securitized commercial loans
Variable Interest Entity [Line Items]
Amount acquired, eliminated in consolidation	$ 65,300
Variable interest entity, amount acquired, eligible risk retention	$ 45,300
RSBC Trust
Variable Interest Entity [Line Items]
Principal balance				73,150		90,788
Financing Receivables Gross Unrealized Loss Accumulated In Investments				1,356		0
MRCD Trust | Securitized commercial loans
Variable Interest Entity [Line Items]
Amount acquired, eliminated in consolidation						161,400
MRCD Trust | Class HRR | Securitized commercial loans
Variable Interest Entity [Line Items]
Amount acquired, eliminated in consolidation						10,500
Financing Receivables Gross Unrealized Loss Accumulated In Investments				43,700
VIE
Variable Interest Entity [Line Items]
Total assets				1,959,017		2,501,179
Securitized commercial loans, at fair value				477,131		909,040
VIE | Securitized commercial loans
Variable Interest Entity [Line Items]
Total assets				583,753		1,061,543
Securitized commercial loans, at fair value				477,131		$ 909,040
VIE | CMSC Trust | Securitized commercial loans
Variable Interest Entity [Line Items]
Total assets				$ 13,400