FINANCIAL INSTRUMENTS - Assets and Liabilities at Fair Value (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Assets:
Total assets	$ 2,334,700,195	$ 2,549,769,851
Liabilities:
Total liabilities	(1,192,956,336)	(1,223,623,061)
Quoted prices in active markets for identical assets Level 1
Assets:
Total assets	18,132,700	5,349,613
Liabilities:
Total liabilities	0	0
Significant other observable inputs Level 2
Assets:
Total assets	2,313,545,946	2,541,456,377
Liabilities:
Total liabilities	(1,192,956,336)	(1,223,623,061)
Unobservable inputs Level 3
Assets:
Total assets	3,021,549	2,963,861
Liabilities:
Total liabilities	0	0
Residential mortgage-backed securities
Assets:
Total assets	1,095,189,264	1,290,825,648
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	1,095,189,264	1,290,825,648
Residential mortgage-backed securities | Unobservable inputs Level 3
Assets:
Total assets	0	0
Multi-Family mortgage loans held in securitization trusts
Assets:
Total assets	1,106,592,612	1,130,874,274
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	1,106,592,612	1,130,874,274
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	111,764,070	119,756,455
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	111,764,070	119,756,455
Residential mortgage loans held in securitization trusts | Unobservable inputs Level 3
Assets:
Total assets	0	0
Mortgage servicing rights
Assets:
Total assets	3,021,549	2,963,861
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	3,021,549	2,963,861
Futures
Assets:
Total assets	18,132,700	5,349,613
Futures | Quoted prices in active markets for identical assets Level 1
Assets:
Total assets	18,132,700	5,349,613
Futures | Significant other observable inputs Level 2
Assets:
Total assets	0	0
Futures | Unobservable inputs Level 3
Assets:
Total assets	0	0
Multi-family securitized debt obligations
Liabilities:
Total liabilities	(1,086,279,589)	(1,109,204,743)
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	(1,086,279,589)	(1,109,204,743)
Multi-family securitized debt obligations | Unobservable inputs Level 3
Liabilities:
Total liabilities	0	0
Residential securitized debt obligations
Liabilities:
Total liabilities	(106,676,747)	(114,418,318)
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	(106,676,747)	(114,418,318)
Residential securitized debt obligations | Unobservable inputs Level 3
Liabilities:
Total liabilities	$ 0	$ 0