SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Changes in Cash Flows Due to Adoption of ASU 2016-15 (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash provided by operating activities	$ 283,024	$ 53,258
Net increase in balance	(447,777)	7,939
Balance	$ 139,516	43,362	$ 587,449	$ 34,665
As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net cash provided by operating activities		49,771
Net increase in balance		4,452
Balance		$ 30,873		$ 25,663