SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 73,380,534	$ 34,347,339
Restricted cash	7,932,233	11,275,263
Total cash, cash equivalents and restricted cash	$ 81,312,767	$ 45,622,602	$ 57,240,715	$ 37,889,596