FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Assets and Liabilities) (Details) - Recurring basis - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Assets:
Assets	$ 41,330	$ 17,358
Cash and cash equivalents
Assets:
Money market funds	37,342	14,518
Other long-term assets
Assets:
Equity, bond, and money market mutual funds held in trust related to the Voluntary Savings Plan	2,453	2,359
Interest rate swaps	1,535	481
Accrued and other long term liabilities
Liabilities:
Contingent consideration	4,092	6,970
Level 1
Assets:
Assets	39,795	16,877
Level 1 | Cash and cash equivalents
Assets:
Money market funds	37,342	14,518
Level 1 | Other long-term assets
Assets:
Equity, bond, and money market mutual funds held in trust related to the Voluntary Savings Plan	2,453	2,359
Level 2
Assets:
Assets	1,535	481
Level 2 | Other long-term assets
Assets:
Interest rate swaps	1,535	481
Level 3 | Accrued and other long term liabilities
Liabilities:
Contingent consideration	$ 4,092	$ 6,970
Level 3 | Accrued and other long term liabilities | LDS
Liabilities:
Discount rate (as a percent)	12.00%	12.50%