SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of restricted cash (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 1,349,831	$ 1,105,787
Restricted cash	1,500,000	0
Cash and cash equivalents and restricted cash as shown in the consolidated statements of cash flows	$ 2,849,831	$ 1,105,787	$ 3,206,158