LONG-TERM DEBT / INTEREST EXPENSE - Schedule of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Debt Instrument
Other	$ (23)	$ (5)	$ 705	$ (50)
Interest expense, net	16,339	15,360	48,300	45,078
Senior Credit Facility
Debt Instrument
Amortization of discount and debt issuance costs	550	591	1,800	1,775
Interest expense	12,541	11,703	36,291	34,271
Senior Credit Facility | Revolving Credit Facility
Debt Instrument
Interest expense (excluding amortization)	1,188	1,359	3,982	3,420
Senior Credit Facility | Term Loan Facility
Debt Instrument
Interest expense (excluding amortization)	10,803	9,753	30,509	29,076
1.5% Convertible Senior Notes, Due 2020 | Convertible Senior Notes
Debt Instrument
Interest expense (excluding amortization)	1,078	1,078	3,210	3,234
Amortization of conversion feature	2,422	2,294	7,156	6,778
Amortization of discount and debt issuance costs	321	290	938	845
Interest expense	$ 3,821	$ 3,662	$ 11,304	$ 10,857