SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Net Loss Per Share (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Common shares not included in the computation of diluted net loss per share
Potentially issuable common shares not included in the computation of diluted net loss per share because they would have an anti-dilutive effect	18,747	9,166
Stock Options
Common shares not included in the computation of diluted net loss per share
Potentially issuable common shares not included in the computation of diluted net loss per share because they would have an anti-dilutive effect	3,284	3,613
Restricted Stock Awards
Common shares not included in the computation of diluted net loss per share
Potentially issuable common shares not included in the computation of diluted net loss per share because they would have an anti-dilutive effect	6,315	5,553
Convertible Notes
Common shares not included in the computation of diluted net loss per share
Potentially issuable common shares not included in the computation of diluted net loss per share because they would have an anti-dilutive effect	9,148