FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Carrying Value
Fair value disclosure
Debt obligations	$ 268,441	$ 243,032
Fair Value
Fair value disclosure
Debt obligations	267,131	242,503
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	35,000
Level 2 | Accounts receivable securitization program | Fair Value
Fair value disclosure
Debt obligations	45,000	35,000
Level 2 | Notes payable | Carrying Value
Fair value disclosure
Debt obligations	153,441	138,032
Level 2 | Notes payable | Fair Value
Fair value disclosure
Debt obligations	$ 152,131	$ 137,503