LONG-TERM DEBT / INTEREST EXPENSE - Schedule of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Debt Instrument
Other	$ 7	$ (29)	$ 728	$ (45)
Interest expense, net	16,067	15,275	31,961	29,718
Senior Credit Facility
Debt Instrument
Amortization of discount and debt issuance costs	625	592	1,250	1,184
Interest expense	12,318	11,694	23,750	22,568
Senior Credit Facility | Revolving Credit Facility
Debt Instrument
Interest expense (excluding amortization)	1,505	1,445	2,794	2,061
Senior Credit Facility | Term Loan Facility
Debt Instrument
Interest expense (excluding amortization)	10,188	9,657	19,706	19,323
1.5% Convertible Senior Notes, Due 2020 | Convertible Senior Notes
Debt Instrument
Interest expense (excluding amortization)	1,054	1,078	2,132	2,156
Amortization of conversion feature	2,377	2,252	4,734	4,484
Amortization of discount and debt issuance costs	311	280	617	555
Interest expense	$ 3,742	$ 3,610	$ 7,483	$ 7,195