SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($)			3 Months Ended		12 Months Ended	13 Months Ended	28 Months Ended
		Mar. 08, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018	Dec. 15, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Maximum exposure to loss from consolidated trusts			$ 25,497,642		$ 27,108,818
Available-for-sale securities	[1]		$ 1,095,189,264		$ 1,290,825,648		$ 1,095,189,264
Backstop deferred income, amortization period			5 years
Backstop guarantee, assumed prepayment rate (percentage)			15.00%
Common stock, shares authorized (in shares)			450,000,000		450,000,000		450,000,000
Common stock, par value (in dollars per share)			$ 0.01		$ 0.01		$ 0.01
Common stock, shares issued (in shares)			23,683,164		22,143,758		23,683,164
Common stock, shares outstanding (in shares)			23,683,164		22,143,758		23,683,164
Stock repurchase program, authorized amount								$ 10,000,000
Preferred stock, shares authorized (in shares)			50,000,000		50,000,000		50,000,000
Preferred stock, par value (in dollars per share)			$ 0.01		$ 0.01		$ 0.01
Preferred stock, shares issued (in shares)			1,610,000		1,610,000		1,610,000
Preferred stock, shares outstanding (in shares)			1,610,000		1,610,000		1,610,000
Income taxes, interest paid			$ 5,242,972	$ 4,147,592
Stock Repurchase Program
Schedule of Trading Securities and Other Trading Assets [Line Items]
Common stock shares repurchased (in shares)			0			126,856	126,856
Weighted average share price of common stock repurchased (in dollars per share)						$ 5.09
Stock repurchase program, remaining authorized amount			$ 9,400,000				$ 9,400,000
Multi-Family MBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale securities					$ 5,742,000
Internal Revenue Service (IRS)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Income taxes, interest paid		$ 2,010,000		2,010,000
Income taxes, interest provision				1,860,000	$ 1,860,000
Income taxes, interest expense		$ 150,000		$ 150,000

[1] Our consolidated balance sheets include assets and liabilities of consolidated variable interest entities ("VIEs") as the Company is the primary beneficiary of these VIEs. As of March 31, 2018 and December 31, 2017, assets of consolidated VIEs totaled $1,223,232,702 and $1,255,404,335 respectively, and the liabilities of consolidated VIEs totaled $1,197,735,060 and $1,228,295,517 respectively