AVAILABLE-FOR-SALE SECURITIES - Components of Interest Income on AFS Securities (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Debt Securities, Available-for-sale [Line Items]
Coupon interest	$ 0	$ 7,870,458	$ 12,152,397	$ 19,655,427
Net (premium amortization)/ discount accretion	0	(43,177)	(1,403,431)	1,653,155
Interest income	0	7,827,281	10,748,966	21,308,582
Agency
Debt Securities, Available-for-sale [Line Items]
Coupon interest	0	7,870,458	12,152,397	19,613,173
Net (premium amortization)/ discount accretion	0	(514,600)	(1,435,534)	(263,230)
Interest income	0	7,355,858	10,716,863	19,349,943
Non-Agency
Debt Securities, Available-for-sale [Line Items]
Coupon interest	0	0	0	42,254
Net (premium amortization)/ discount accretion	0	0	0	9,946
Interest income	0	0	0	52,200
Multi-Family
Debt Securities, Available-for-sale [Line Items]
Coupon interest	0	0	0	0
Net (premium amortization)/ discount accretion	0	471,423	32,103	1,906,439
Interest income	$ 0	$ 471,423	$ 32,103	$ 1,906,439