Note 6 - CMBS Structured Pass Through Certificates - Summary of CMBS I/O Strips (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2021	Dec. 31, 2020
CMBS structured pass through certificates, at fair value		$ 72,645	$ 38,984
Multifamily [Member] | CMBS I/O Strip, One [Member]
CMBS structured pass through certificates, at fair value		$ 2,432
Interest rate		2.09%
Current yield	[1]	14.95%
Multifamily [Member] | CMBS I/O Strip, Two [Member]
CMBS structured pass through certificates, at fair value		$ 8,712
Interest rate		0.10%
Current yield	[1]	14.34%
Multifamily [Member] | CMBS I/O Strip, Three [Member]
CMBS structured pass through certificates, at fair value		$ 23,783
Interest rate		3.09%
Current yield	[1]	14.64%
Multifamily [Member] | CMBS I/O Strip, Four [Member]
CMBS structured pass through certificates, at fair value		$ 7,437
Interest rate		1.71%
Current yield	[1]	14.77%
Multifamily [Member] | CMBS I/O Strip, Five [Member]
CMBS structured pass through certificates, at fair value		$ 4,919
Interest rate		3.50%
Current yield	[1]	14.31%
Multifamily [Member] | CMBS I/O Strip, Six [Member]
CMBS structured pass through certificates, at fair value		$ 611
Interest rate		2.39%
Current yield	[1]	16.61%
Multifamily [Member] | CMBS IO Strip Seven [Member]
CMBS structured pass through certificates, at fair value		$ 7,289
Interest rate		1.39%
Current yield	[1]	15.32%
Multifamily [Member] | CMBS IO Strip Eight [Member]
CMBS structured pass through certificates, at fair value		$ 1,975
Interest rate		1.31%
Current yield	[1]	18.42%
Multifamily [Member] | CMBS I/O Strip, Nine [Member]
CMBS structured pass through certificates, at fair value		$ 3,345
Interest rate		1.96%
Multifamily [Member] | CMBS I/O Strip, Ten [Member]
CMBS structured pass through certificates, at fair value		$ 1,734
Interest rate		3.20%
Current yield	[1]	14.45%
Multifamily [Member] | CMBS I/O Strip, Eleven [Member]
CMBS structured pass through certificates, at fair value		$ 325
Interest rate		2.70%
Current yield	[1]	12.72%
Multifamily [Member] | CMBS I/O Strip, Twelve [Member]
CMBS structured pass through certificates, at fair value		$ 5,058
Interest rate		2.04%
Current yield	[1]	13.30%
Multifamily [Member] | CMBS I/O Strip, Thirteen [Member]
CMBS structured pass through certificates, at fair value		$ 5,025
Interest rate		2.95%
Current yield	[1]	14.06%
Multifamily [Member] | CMBS I/O Strip, Fourteen [Member]
Current yield	[1]	12.30%
Multifamily [Member] | Collateralized Mortgage Backed Securities [Member]
CMBS structured pass through certificates, at fair value		$ 72,645
Current yield	[1]

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