SHARE-BASED COMPENSATION - RSU Activity - Summary of Change (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Restricted Stock Units [Roll Forward]
RSUs beginning	2,074,794
RSUs awarded	808,443	1,123,000	796,000
RSUs assumed in Merger	2,255,312
RSUs released	(474,069)	(611,000)	(406,000)
RSUs forfeited	(379,190)	(27,000)	(58,000)
RSUs ending	4,285,290	2,074,794
Weighted Average Purchase Price RSUs	$ 0
Weighted Average Remaining Contractual Term (Years) RSUs	1 year 2 months 12 days
Aggregate Intrinsic Value RSUs	$ 23,870,025
Number of RSUs vested and expected to vest	4,112,791
Weighted Average Purchase Price of RSUs vested and expected to vest	$ 0
Weighted Average Remaining Contractual Term (Years) of RUSs vested and expected to vest	1 year 2 months 12 days
Aggregate Intrinsic Value RSUs vested and expected to vest	$ 23,090,689
Number of RSUs exercisable	48,880
Weighted Average Purchase Price of RUSs exercisable	$ 0
Weighted Average Remaining Contractual Term (Years) of RUSs exercisable	0 years
Aggregate Intrinsic Value RSUs exercisable	$ 537,680
Weighted average remaining recognition period in years	2 years 1 month 6 days
Unamortized compensation expense, net of estimated forfeitures	$ 26,899,098