FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Debt) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Carrying Value
Fair value disclosure
Debt obligations	$ 249,258	$ 268,441
Fair Value
Fair value disclosure
Debt obligations	247,522	267,131
Level 2 | Credit Facility | Carrying Value
Fair value disclosure
Debt obligations	70,000	70,000
Level 2 | Credit Facility | Fair Value
Fair value disclosure
Debt obligations	70,000	70,000
Level 2 | Accounts receivable securitization program | Carrying Value
Fair value disclosure
Debt obligations	45,000	45,000
Level 2 | Accounts receivable securitization program | Fair Value
Fair value disclosure
Debt obligations	45,000	45,000
Level 2 | Notes payable | Carrying Value
Fair value disclosure
Debt obligations	134,258	153,441
Level 2 | Notes payable | Fair Value
Fair value disclosure
Debt obligations	$ 132,522	$ 152,131