FAIR VALUE MEASUREMENTS - Summary of fair value Level 3 debt - Term loan (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Term loan	$ 430,232	$ 298,500
Revolving credit facility	18,500	5,000
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Term loan	433,998	301,485
Revolving credit facility	$ 18,662	$ 5,050