FINANCIAL INSTRUMENTS - Assets and Liabilities at Fair Value (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Assets:
Total assets	$ 2,549,769,851	$ 2,249,305,912
Liabilities:
Total liabilities	(1,223,623,061)	(1,339,430,026)
Quoted prices in active markets for identical assets Level 1
Assets:
Total assets	5,349,613	8,053,813
Liabilities:
Total liabilities	0	0
Significant other observable inputs Level 2
Assets:
Total assets	2,541,456,377	2,237,811,290
Liabilities:
Total liabilities	(1,223,623,061)	(1,339,430,026)
Unobservable inputs Level 3
Assets:
Total assets	2,963,861	3,440,809
Liabilities:
Total liabilities	0	0
Residential mortgage-backed securities
Assets:
Total assets	1,290,825,648	870,929,601
Residential mortgage-backed securities | Quoted prices in active markets for identical assets Level 1
Assets:
Total assets	0	0
Residential mortgage-backed securities | Significant other observable inputs Level 2
Assets:
Total assets	1,290,825,648	870,929,601
Residential mortgage-backed securities | Unobservable inputs Level 3
Assets:
Total assets	0	0
Residential mortgage loans
Assets:
Total assets	0	2,849,536
Residential mortgage loans | Quoted prices in active markets for identical assets Level 1
Assets:
Total assets	0	0
Residential mortgage loans | Significant other observable inputs Level 2
Assets:
Total assets	0	2,849,536
Residential mortgage loans | Unobservable inputs Level 3
Assets:
Total assets	0	0
Multi-Family mortgage loans held in securitization trusts
Assets:
Total assets	1,130,874,274	1,222,905,433
Multi-Family mortgage loans held in securitization trusts | Quoted prices in active markets for identical assets Level 1
Assets:
Total assets	0	0
Multi-Family mortgage loans held in securitization trusts | Significant other observable inputs Level 2
Assets:
Total assets	1,130,874,274	1,222,905,433
Multi-Family mortgage loans held in securitization trusts | Unobservable inputs Level 3
Assets:
Total assets	0	0
Residential mortgage loans held in securitization trusts
Assets:
Total assets	119,756,455	141,126,720
Residential mortgage loans held in securitization trusts | Quoted prices in active markets for identical assets Level 1
Assets:
Total assets	0	0
Residential mortgage loans held in securitization trusts | Significant other observable inputs Level 2
Assets:
Total assets	119,756,455	141,126,720
Residential mortgage loans held in securitization trusts | Unobservable inputs Level 3
Assets:
Total assets	0	0
Mortgage servicing rights
Assets:
Total assets	2,963,861	3,440,809
Mortgage servicing rights | Quoted prices in active markets for identical assets Level 1
Assets:
Total assets	0	0
Mortgage servicing rights | Significant other observable inputs Level 2
Assets:
Total assets	0	0
Mortgage servicing rights | Unobservable inputs Level 3
Assets:
Total assets	2,963,861	3,440,809
Eurodollar Futures
Assets:
Total assets	5,349,613	8,053,813
Eurodollar Futures | Quoted prices in active markets for identical assets Level 1
Assets:
Total assets	5,349,613	8,053,813
Eurodollar Futures | Significant other observable inputs Level 2
Assets:
Total assets	0	0
Eurodollar Futures | Unobservable inputs Level 3
Assets:
Total assets	0	0
Multi-family securitized debt obligations
Liabilities:
Total liabilities	(1,109,204,743)	(1,204,583,678)
Multi-family securitized debt obligations | Quoted prices in active markets for identical assets Level 1
Liabilities:
Total liabilities	0	0
Multi-family securitized debt obligations | Significant other observable inputs Level 2
Liabilities:
Total liabilities	(1,109,204,743)	(1,204,583,678)
Multi-family securitized debt obligations | Unobservable inputs Level 3
Liabilities:
Total liabilities	0	0
Residential securitized debt obligations
Liabilities:
Total liabilities	(114,418,318)	(134,846,348)
Residential securitized debt obligations | Quoted prices in active markets for identical assets Level 1
Liabilities:
Total liabilities	0	0
Residential securitized debt obligations | Significant other observable inputs Level 2
Liabilities:
Total liabilities	(114,418,318)	(134,846,348)
Residential securitized debt obligations | Unobservable inputs Level 3
Liabilities:
Total liabilities	$ 0	$ 0