FINANCIAL INSTRUMENTS - Assets and Liabilities at Fair Value (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Assets:
Total assets	$ 2,583,267,939	$ 2,249,305,912
Liabilities:
Total liabilities	(1,249,184,941)	(1,339,430,026)
Quoted prices in active markets for identical assets Level 1
Assets:
Total assets	0	8,053,813
Liabilities:
Total liabilities	(529,075)	0
Significant other observable inputs Level 2
Assets:
Total assets	2,580,273,942	2,237,811,290
Liabilities:
Total liabilities	(1,248,655,866)	(1,339,430,026)
Unobservable inputs Level 3
Assets:
Total assets	2,993,997	3,440,809
Liabilities:
Total liabilities	0	0
Residential mortgage-backed securities
Assets:
Total assets	1,304,486,040	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	1,304,486,040	870,929,601
Residential mortgage-backed securities | Unobservable inputs Level 3
Assets:
Total assets	0	0
Residential mortgage loans
Assets:
Total assets	495,486	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	495,486	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	1,149,888,917	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	1,149,888,917	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	125,403,499	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	125,403,499	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	2,993,997	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	2,993,997	3,440,809
Multi-family securitized debt obligations
Liabilities:
Total liabilities	(1,128,773,402)	(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	(1,128,773,402)	(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	(119,882,464)	(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	(119,882,464)	(134,846,348)
Residential securitized debt obligations | Unobservable inputs Level 3
Liabilities:
Total liabilities	0	0
Futures
Assets:
Total assets		8,053,813
Liabilities:
Total liabilities	(529,075)
Futures | Quoted prices in active markets for identical assets Level 1
Assets:
Total assets		8,053,813
Liabilities:
Total liabilities	(529,075)
Futures | Significant other observable inputs Level 2
Assets:
Total assets		0
Liabilities:
Total liabilities	0
Futures | Unobservable inputs Level 3
Assets:
Total assets		$ 0
Liabilities:
Total liabilities	$ 0