FAIR VALUE MEASUREMENT - Narrative (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Fourth Quarter Acquisitions, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration related to 2017 and 2018 acquisitions	$ 2,233
Contingent consideration, percent of contractual amount of acquisitions recognized	51.00%
Third Quarter Acquisitions, 2018 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration related to 2017 and 2018 acquisitions	$ 4,500
Contingent consideration, percent of contractual amount of acquisitions recognized	100.00%