Income Taxes - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Apr. 30, 2020	Apr. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Income Tax [Line Items]
Excise tax percentage			100.00%		100.00%
Reserve for uncertain income tax positions			$ 0		$ 0		$ 0
Interest for underpayment of income taxes			0		0
Penalties for underpayment of income taxes			0		0
Current portion of income tax expense (benefit)			200,000	$ 100,000	$ 1,400,000	$ 200,000
Effective income tax rate					1.50%	0.20%
Aggregate losses from the sales						$ 1,051,000
CRE Debt Securities
Income Tax [Line Items]
Aggregate face value of debt securities	$ 969,800,000	$ 782,000,000.0
Proceeds from sale of debt securities, gross	$ 766,400,000	614,800,000
Aggregate losses from the sales		$ 167,300,000			$ 203,400,000
CRE Debt Securities | Minimum
Income Tax [Line Items]
Percentage of REIT taxable income distributed to stockholders					90.00%
TRSs
Income Tax [Line Items]
Deferred tax assets			0		$ 0		0
Deferred tax liabilities			$ 200,000		$ 200,000		$ 0
REIT Subsidiaries
Income Tax [Line Items]
Equity interest percentage by parent			100.00%		100.00%
Sub-REIT
Income Tax [Line Items]
Equity interest percentage by parent			100.00%		100.00%
U.S. federal corporate tax rate					21.00%