AVAILABLE-FOR-SALE SECURITIES - Realized Gain (Loss) from Sale of AFS Securities (Details) - AFS Securities - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
AFS securities sold, at cost	$ 6,832,799	$ 102,654,599	$ 62,435,106	$ 191,586,798
AFS principal payments, at cost	0	19,599,985	0	34,136,121
Proceeds from AFS securities sold	6,681,250	106,681,346	52,966,554	189,273,268
Proceeds from AFS principal payments	0	19,344,386	0	33,837,646
Net realized gain (loss) on sale of AFS securities	$ (151,549)	$ 3,771,148	$ (9,468,552)	$ (2,612,005)