FAIR VALUE MEASUREMENT (Narrative) (Details) - Fair Value, Inputs, Level 3 [Member] $ in Millions	Mar. 31, 2018 USD ($)
4.5% Convertible Notes [Member]
Convertible Debt, Fair Value Disclosures	$ 5.7
4.50% Convertible Notes 2013 [Member]
Debt Instrument, Face Amount	5.9
7.50% Convertible Notes 2016 [Member]
Convertible Debt, Fair Value Disclosures	69.3
Debt Instrument, Face Amount	$ 58.1

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant