AVAILABLE-FOR-SALE SECURITIES - Changes of Unamortized Net Discount and Designated Credit Reserves (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Designated credit reserve
Beginning Balance	$ 0	$ (1,929,833)
Dispositions	0	1,929,833
Accretion of net discount	0	0
Ending Balance	0	0
Unamortized net discount
Beginning Balance	(2,204,562)	(27,841,262)
Dispositions	2,042,842	22,685,756
Accretion of net discount	161,720	2,950,944
Ending Balance	0	(2,204,562)
Total
Beginning Balance	(2,204,562)	(29,771,095)
Dispositions	2,042,842	24,615,589
Accretion of net discount	161,720	2,950,944
Ending Balance	$ 0	$ (2,204,562)