SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Changes in Cash Flows Due to Adoption of ASU 2016-15 (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash provided by (used in) operating activities	$ 211,553	$ 54,282
Net decrease in balance	(361,543)	(12,147)
Balance	$ 225,654	22,648	$ 587,449	$ 34,665
As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash provided by (used in) operating activities		53,871
Net decrease in balance		(12,558)
Balance		$ 13,235		$ 25,663