Note 6 - CMBS Structured Pass Through Certificates - Summary of CMBS I/O Strips (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2022		Dec. 31, 2021
CMBS structured pass-through certificates, at fair value		$ 68,133		$ 69,816
Multifamily [Member] | CMBS I/O Strip, One [Member]
CMBS structured pass-through certificates, at fair value		$ 2,170		$ 2,356
Interest rate		2.02%		2.02%
Current yield	[1]	14.49%		14.47%
Multifamily [Member] | CMBS I/O Strip, Two [Member]
CMBS structured pass-through certificates, at fair value		$ 7,799		$ 8,383
Interest rate		0.10%		0.10%
Current yield	[1]	15.02%		14.67%
Multifamily [Member] | CMBS I/O Strip, Three [Member]
CMBS structured pass-through certificates, at fair value		$ 21,807		$ 23,188
Interest rate		2.98%		2.98%
Current yield	[1]	14.83%		14.48%
Multifamily [Member] | CMBS I/O Strip, Four [Member]
CMBS structured pass-through certificates, at fair value		$ 6,715	[2]	$ 7,274	[3]
Interest rate		1.59%		1.59%
Current yield	[1]	14.27%		13.88%
Multifamily [Member] | CMBS I/O Strip, Five [Member]
CMBS structured pass-through certificates, at fair value		$ 4,403		$ 4,781
Interest rate		3.38%		3.38%
Current yield	[1]	14.50%		14.16%
Multifamily [Member] | CMBS I/O Strip, Six [Member]
CMBS structured pass-through certificates, at fair value		$ 543		$ 589
Interest rate		2.31%		2.31%
Current yield	[1]	17.08%		16.56%
Multifamily [Member] | CMBS IO Strip Seven [Member]
CMBS structured pass-through certificates, at fair value		$ 9,231	[4]	$ 6,424	[5]
Interest rate		1.25%		1.26%
Current yield		14.27%	[1]	13.57%
Multifamily [Member] | CMBS IO Strip Eight [Member]
CMBS structured pass-through certificates, at fair value		$ 1,649		$ 1,850
Interest rate		1.19%		1.20%
Current yield		16.73%	[1]	17.02%
Multifamily [Member] | CMBS I/O Strip, Nine [Member]
CMBS structured pass-through certificates, at fair value		$ 2,989		$ 3,246
Interest rate		1.89%		1.89%
Current yield				14.30%
Multifamily [Member] | CMBS I/O Strip, Ten [Member]
CMBS structured pass-through certificates, at fair value		$ 1,575		$ 1,697
Interest rate		3.10%		3.10%
Current yield		14.66%	[1]	12.55%
Multifamily [Member] | CMBS I/O Strip, Eleven [Member]
CMBS structured pass-through certificates, at fair value		$ 294		$ 317
Interest rate		2.61%		2.61%
Current yield		12.81%	[1]	13.14%
Multifamily [Member] | CMBS I/O Strip, Twelve [Member]
CMBS structured pass-through certificates, at fair value		$ 4,424		$ 4,827
Interest rate		1.92%		1.92%
Current yield		13.43%	[1]	13.53%
Multifamily [Member] | CMBS I/O Strip, Thirteen [Member]
CMBS structured pass-through certificates, at fair value		$ 4,534		$ 4,884
Interest rate		2.95%		2.95%
Current yield		13.86%	[1]	12.55%
Multifamily [Member] | CMBS I/O Strip, Fourteen [Member]
Current yield	[1]	12.82%
Multifamily [Member] | Collateralized Mortgage-Backed Securities [Member]
CMBS structured pass-through certificates, at fair value		$ 68,133		$ 69,816
Interest rate		2.11%		2.15%
Current yield	[1]	14.49%		14.16%

[1] Current yield is the annualized income earned divided by the cost basis of the investment.

[2] The Company, through the Subsidiary OPs, purchased approximately $50.0 million and $15.0 million aggregate notional amount of the X1 interest-only tranche of the FHMS K-107 CMBS I/O Strip on April 28, 2021 and May 4, 2021, respectively.

[3] The Company, through the Subsidiary OPs, purchased approximately $50.0 million and $15.0 million aggregate notional amount of the X1 interest-only tranche of the FHMS K-107 CMBS I/O Strip on April 28, 2021 and May 4, 2021, respectively.

[4] The Company, through the Subsidiary OPs, purchased approximately $80.0 million, $35.0 million, $40.0 million and $50.0 million aggregate notional amount of the X1 interest-only tranche of the FRESB 2019-SB64 CMBS I/O Strip on June 11, 2021, September 29, 2021, February 3, 2022 and March 18, 2022, respectively.

[5] The Company, through the Subsidiary OPs, purchased approximately $80.0 million and $35.0 million aggregate notional amount of the X1 interest-only tranche of the FRESB 2019-SB64 CMBS I/O Strip on June 11, 2021 and September 29, 2021, respectively.