LONG-TERM DEBT - Narrative (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument
Outstanding balance	$ 264,688	$ 275,000
Term Loan | Term Loan
Debt Instrument
Term of debt instrument	5 years
Outstanding balance	$ 264,700	$ 275,000
Interest rate (as a percent)	4.10%	3.38%
Term Loan | Term Loan | Minimum
Debt Instrument
Interest coverage ratio	2.5
Term Loan | Term Loan | Maximum
Debt Instrument
Net leverage ratio	4.5
Term Loan | Term Loan | LIBOR
Debt Instrument
Interest rate (as a percent)	1.75%	2.00%
Term Loan | Term Loan | Quarterly Payments for First Three Years | Base Rate
Debt Instrument
Interest rate (as a percent)	1.25%
Term Loan | Term Loan | Quarterly Payments in Fourth Year | Base Rate
Debt Instrument
Interest rate (as a percent)	2.50%
Term Loan | Term Loan | Quarterly Payments in Fifth Year | Base Rate
Debt Instrument
Interest rate (as a percent)	3.75%