SUBSEQUENT EVENTS (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
Feb. 28, 2019	Dec. 31, 2016
SUBSEQUENT EVENTS
Repayment of outstanding balance		$ 19,667
Subsequent event \| Senior convertible notes
SUBSEQUENT EVENTS
Repayment of outstanding balance	$ 127,500

The cash outflow from the repayment of a long-term debt instrument which can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3291-108585

Name:	us-gaap_RepaymentsOfConvertibleDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration