Note 9 - Fair Value of Financial Instruments - Schedule of Carrying Values and Fair Values of Financial Assets and Liabilities Recorded at Fair Value on a Recurring Basis (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020	Feb. 11, 2020
Common stock investment, at fair value	$ 49,321,000	$ 44,626,000
CMBS structured pass through certificates, at fair value	72,645,000	$ 38,984,000
Reported Value Measurement [Member]
Cash and cash equivalents			$ 302
Loan			22,127
Accrued interest and dividends			3,616
Assets, Fair Value Disclosure			2,719,837
Financial and Nonfinancial Liabilities, Fair Value Disclosure			2,539,724
Reported Value Measurement [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Bonds payable held in variable interest entities, at fair value			1,655,960
Reported Value Measurement [Member] | Mortgages [Member]
Loan			863,564
Reported Value Measurement [Member] | Mortgages [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Loan			$ 1,790,228
Fair Value, Recurring [Member]
Cash and cash equivalents	22,219,000
Restricted Cash	2,360,000
Loan	152,633,000
Common stock investment, at fair value	49,321,000
Accrued interest and dividends	6,440,000
CMBS structured pass through certificates, at fair value	72,645,000
Other assets	1,108,000
Assets, Fair Value Disclosure	8,297,872,000
Secured financing agreements, net	831,822,000
Master repurchase agreements	222,533,000
Unsecured Notes	108,030,000
Accounts payable and other accrued liabilities	3,984,000
Accrued interest payable	5,046,000
Due to brokers for securities purchased, not yet settled	2,188,000
Financial and Nonfinancial Liabilities, Fair Value Disclosure	7,826,307,000
Fair Value, Recurring [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Bonds payable held in variable interest entities, at fair value	6,652,704,000
Fair Value, Recurring [Member] | Mortgages [Member]
Loan	873,177,000
Fair Value, Recurring [Member] | Mortgages [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Loan	7,085,361,000
Fair Value, Recurring [Member] | Bridge Loan [Member]
Loan	32,608,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	22,219,000
Restricted Cash	2,360,000
Loan	0
Common stock investment, at fair value	0
Accrued interest and dividends	6,440,000
CMBS structured pass through certificates, at fair value	0
Other assets	1,108,000
Assets, Fair Value Disclosure	32,127,000
Secured financing agreements, net	0
Master repurchase agreements	0
Unsecured Notes	0
Accounts payable and other accrued liabilities	3,984,000
Accrued interest payable	5,046,000
Due to brokers for securities purchased, not yet settled	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	9,030,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Bonds payable held in variable interest entities, at fair value	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgages [Member]
Loan	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgages [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Loan	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Bridge Loan [Member]
Loan	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Cash and cash equivalents	0
Restricted Cash	0
Loan	0
Common stock investment, at fair value	0
Accrued interest and dividends	0
CMBS structured pass through certificates, at fair value	72,645,000
Other assets	0
Assets, Fair Value Disclosure	7,158,006,000
Secured financing agreements, net	0
Master repurchase agreements	0
Unsecured Notes	0
Accounts payable and other accrued liabilities	0
Accrued interest payable	0
Due to brokers for securities purchased, not yet settled	2,188,000
Financial and Nonfinancial Liabilities, Fair Value Disclosure	6,654,892,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Bonds payable held in variable interest entities, at fair value	6,652,704,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgages [Member]
Loan	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgages [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Loan	7,085,361,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Bridge Loan [Member]
Loan	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Cash and cash equivalents	0
Restricted Cash	0
Loan	152,633,000
Common stock investment, at fair value	49,321,000
Accrued interest and dividends	0
CMBS structured pass through certificates, at fair value	0
Other assets	0
Assets, Fair Value Disclosure	1,107,739,000
Secured financing agreements, net	831,822,000
Master repurchase agreements	222,533,000
Unsecured Notes	108,030,000
Accounts payable and other accrued liabilities	0
Accrued interest payable	0
Due to brokers for securities purchased, not yet settled	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	1,162,385,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Bonds payable held in variable interest entities, at fair value	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgages [Member]
Loan	873,177,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgages [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Loan	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Bridge Loan [Member]
Loan	32,608,000
Fair Value, Recurring [Member] | Reported Value Measurement [Member]
Cash and cash equivalents	22,219,000
Restricted Cash	2,360,000
Loan	152,634,000
Common stock investment, at fair value	49,321,000
Accrued interest and dividends	6,440,000
CMBS structured pass through certificates, at fair value	72,645,000
Other assets	1,108,000
Assets, Fair Value Disclosure	8,296,407,000
Secured financing agreements, net	805,427,000
Master repurchase agreements	222,533,000
Unsecured Notes	108,030,000
Accounts payable and other accrued liabilities	3,984,000
Accrued interest payable	5,046,000
Due to brokers for securities purchased, not yet settled	2,188,000
Financial and Nonfinancial Liabilities, Fair Value Disclosure	7,799,912,000
Fair Value, Recurring [Member] | Reported Value Measurement [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Bonds payable held in variable interest entities, at fair value	6,652,704,000
Fair Value, Recurring [Member] | Reported Value Measurement [Member] | Mortgages [Member]
Loan	871,711,000
Fair Value, Recurring [Member] | Reported Value Measurement [Member] | Mortgages [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Loan	7,085,361,000
Fair Value, Recurring [Member] | Reported Value Measurement [Member] | Bridge Loan [Member]
Loan	$ 32,608,000