SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - SOFTWARE COSTS (Details) $ in Millions	Jun. 30, 2019 USD ($)
Operation and maintenance
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Capitalized software costs	$ 3.7
Other noncurrent assets
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Capitalized software costs	$ 1.7

The carrying amount of capitalized computer software costs net of accumulated amortization as of the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

Name:	us-gaap_CapitalizedComputerSoftwareNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant