AVAILABLE-FOR-SALE SECURITIES - Narrative (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Credit-related OTTI losses	$ 3,074,728	$ 3,074,728	$ 3,636,431	$ 0
Gross unrealized (loss)	$ 13,369,252	$ 10,240,388
Number of AFS securities, unrealized loss position for more than twelve months | security	59	46
Number of AFS securities, unrealized loss position for less than twelve months | security	49	31
Number of AFS securities | security	5	5
Unrealized gains (losses) on AFS securities	$ (5,785,854)	$ (8,872,859)	(7,604,122)
AFS Securities
Schedule of Available-for-sale Securities [Line Items]
Unrealized gains (losses) on AFS securities	5,785,854	8,872,859	7,604,122
Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Credit-related OTTI losses	0	730,000
Gross unrealized (loss)	$ 0	$ 0	$ 1,800,000