SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Net Loss Per Share (Details) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
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	18,707	21,274
Option Plan Shares
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	2,387	2,918
Restricted Stock
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	4,123	6,312
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	12,197	12,044