FINANCING ARRANGEMENTS - Schedule of Long-term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Debt Instrument [Line Items]
Net carrying amount of Senior Term Notes	$ 120,435		$ 120,002
Less current portion (included in accrued expenses)	0		(2)
Long-term portion	$ 120,435		$ 120,000
Senior Notes | Senior term notes - 5.75%
Debt Instrument [Line Items]
Interest rate %	0.00%	5.75%	5.75%
Net carrying amount of Senior Term Notes	$ 0		$ 120,000
Senior Notes | Senior term notes - 5.50%
Debt Instrument [Line Items]
Interest rate %	5.50%	5.50%	0.00%
Net carrying amount of Senior Term Notes	$ 120,435		$ 0
Revolving credit facility | Revolving credit facility
Debt Instrument [Line Items]
Interest rate %	0.00%		0.00%
Net carrying amount of Senior Term Notes	$ 0		$ 0
Equipment and leasehold notes payable | Equipment and leasehold notes payable
Debt Instrument [Line Items]
Net carrying amount of Senior Term Notes	$ 0		$ 2
Equipment and leasehold notes payable | Equipment and leasehold notes payable | Minimum
Debt Instrument [Line Items]
Interest rate %	4.90%		4.90%
Equipment and leasehold notes payable | Equipment and leasehold notes payable | Maximum
Debt Instrument [Line Items]
Interest rate %	8.75%		8.75%