FAIR VALUE MEASUREMENTS - Summary of fair value Level 3 debt - Term loan (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Term loan	$ 431,321	$ 298,500
Revolving credit facility	16,000	5,000
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Term loan	435,096	301,485
Revolving credit facility	$ 16,140	$ 5,050