AVAILABLE-FOR-SALE SECURITIES - Components of Interest Income on AFS Securities (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Coupon interest	$ 22,720,000	$ 22,627,000	$ 21,595,000	$ 22,191,000	$ 22,162,000	$ 22,733,000	$ 23,610,000	$ 24,617,000	$ 28,046,192	$ 16,724,278	$ 11,087,306
Investment Income, Net, Amortization Of Discount And Premium, Before Adjustment										6,751,487	13,210,850
Net (premium amortization)/ discount accretion									1,475,701	6,751,667	13,210,849
Interest income									29,521,893	23,475,765	24,298,156
Agency
Schedule of Available-for-sale Securities [Line Items]
Coupon interest									28,003,938	13,138,828	7,286,166
Net (premium amortization)/ discount accretion									(654,970)	341,020	241,550
Interest income									27,348,968	13,479,848	7,527,716
Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Coupon interest									42,254	2,579,344	2,357,814
Net (premium amortization)/ discount accretion									9,946	1,343,594	7,653,839
Interest income									52,200	3,922,938	10,011,653
Multi-Family
Schedule of Available-for-sale Securities [Line Items]
Coupon interest									0	1,006,106	1,443,326
Net (premium amortization)/ discount accretion									2,120,725	5,066,873	5,315,461
Interest income									$ 2,120,725	$ 6,072,979	$ 6,758,787