AVAILABLE-FOR-SALE SECURITIES - Carrying Value of AFS Securities Not Deemed to be Other Than Temporarily Impaired (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Less than 12 months, Estimated Fair Value	$ 1,084,010,586	$ 619,414,077
Less than 12 months, Gross Unrealized Losses	(11,135,736)	(8,129,704)
Greater than 12 months, Estimated Fair Value	95,024,791	45,879,433
Greater than 12 months, Gross Unrealized Losses	(2,233,516)	(2,110,684)
Total, Estimated Fair Value	1,179,035,377	665,293,510
Total, Gross Unrealized Losses	$ (13,369,252)	$ (10,240,388)