SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($)			3 Months Ended	9 Months Ended		12 Months Ended	13 Months Ended
		Mar. 08, 2017	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 15, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Maximum exposure to loss from consolidated trusts				$ 26,740,446		$ 24,716,861
Fair value of investments	[1]			$ 1,304,486,040		$ 870,929,601	$ 870,929,601
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)				22,139,258		17,539,258	17,539,258
Common stock, shares outstanding (in shares)				22,139,258		17,539,258	17,539,258
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				$ 11,086,534	$ 4,671,932
Stock Repurchase Program
Schedule of Trading Securities and Other Trading Assets [Line Items]
Common stock shares repurchased (in shares)				0			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
Non-Agency
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments				0		$ 7,592,802	$ 7,592,802
Maximum loss exposure from VIEs				0		4,413,403	4,413,403
Multi-Family MBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments				$ 30,750,419		73,146,566	73,146,566
Residential mortgage loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unpaid mortgage balance								$ 518,455,163
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	$ 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 September 30, 2017 and December 31, 2016, assets of consolidated VIEs totaled $1,280,093,874 and $1,369,120,941 respectively, and the liabilities of consolidated VIEs totaled $1,253,353,428 and $1,344,404,080 respectively