DERIVATIVE INSTRUMENTS HEDGING AND NON-HEDGING ACTIVITIES - Gains and Losses on Derivative Contracts (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
Interest rate:
Amount of realized gain (loss)									$ 2,219,719	$ (3,089,001)	$ (12,024,730)
Amount of unrealized appreciation (depreciation)									(2,704,413)	5,495,463	4,909,858
Total									(484,694)	2,406,462	(7,114,872)
Net interest income	$ 4,782,000	$ 4,746,000	$ 4,828,000	$ 5,784,000	$ 5,903,000	$ 6,153,000	$ 5,772,000	$ 5,760,000	20,139,551	23,588,344	31,309,716
Interest expense	17,938,000	17,881,000	16,767,000	16,408,000	16,259,000	16,580,000	17,837,000	18,857,000
Interest income	$ 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
Eurodollar Futures
Interest rate:
Amount of realized gain (loss)									2,219,719	(3,089,001)	(4,892,855)
Amount of unrealized appreciation (depreciation)									(2,704,413)	5,495,463	3,092,300
Total									$ (484,694)	$ 2,406,462	(1,800,555)
Interest Rate Swaps
Interest rate:
Amount of realized gain (loss)											(7,047,875)
Amount of unrealized appreciation (depreciation)											1,755,108
Total											(5,292,767)
Swaptions
Interest rate:
Amount of realized gain (loss)											(84,000)
Amount of unrealized appreciation (depreciation)											62,450
Total											(21,550)
Swaps
Interest rate:
Net interest income											2,216,417
Interest expense											2,719,563
Interest income											$ 503,146