Note 4 - CMBS Trusts - Schedule of Geographies and Property Types of Collateral Underlying the CMBS Trusts as Percentage of Collateral Unpaid Principal Balance (Details) - Variable Interest Entity, Primary Beneficiary [Member]	Sep. 30, 2021	Dec. 31, 2020
Percentage of Collateral Unpaid Principal Balance	100.00%	100.00%
Multifamily [Member]
Percentage of Collateral Unpaid Principal Balance	98.26%	98.12%
Manufactured Housing [Member]
Percentage of Collateral Unpaid Principal Balance	1.74%	1.88%
TEXAS
Percentage of Collateral Unpaid Principal Balance	16.38%	15.02%
FLORIDA
Percentage of Collateral Unpaid Principal Balance	14.38%	16.25%
ARIZONA
Percentage of Collateral Unpaid Principal Balance	8.94%	11.80%
CALIFORNIA
Percentage of Collateral Unpaid Principal Balance	7.31%	8.25%
GEORGIA
Percentage of Collateral Unpaid Principal Balance	6.67%	7.05%
WASHINGTON
Percentage of Collateral Unpaid Principal Balance	6.66%	5.76%
NEW JERSEY
Percentage of Collateral Unpaid Principal Balance	4.76%	4.14%
NEVADA
Percentage of Collateral Unpaid Principal Balance	3.60%	4.12%
PENNSYLVANIA
Percentage of Collateral Unpaid Principal Balance		3.30%
COLORADO
Percentage of Collateral Unpaid Principal Balance	4.18%	2.26%
CONNECTICUT
Percentage of Collateral Unpaid Principal Balance	3.10%
NORTH CAROLINA
Percentage of Collateral Unpaid Principal Balance	2.91%	1.98%
NEW YORK
Percentage of Collateral Unpaid Principal Balance	2.66%	3.00%
OHIO
Percentage of Collateral Unpaid Principal Balance	1.77%	2.00%
VIRGINIA
Percentage of Collateral Unpaid Principal Balance	1.74%	2.09%
INDIANA
Percentage of Collateral Unpaid Principal Balance	1.72%	2.42%
SOUTH CAROLINA
Percentage of Collateral Unpaid Principal Balance	1.59%	1.08%
UTAH
Percentage of Collateral Unpaid Principal Balance		1.33%
MARYLAND
Percentage of Collateral Unpaid Principal Balance	1.59%	1.32%
MISSOURI
Percentage of Collateral Unpaid Principal Balance	1.29%	1.20%
TENNESSEE
Percentage of Collateral Unpaid Principal Balance	1.21%	1.45%
Other [Member]
Percentage of Collateral Unpaid Principal Balance	7.54%	4.21%