SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Liabilities:
Long term debt	$ 118,100		$ 125,300
Change in the contingent consideration liability
Beginning Balance	6,073	$ 4,019
Payment of contingent consideration	(3,386)	(2,483)
Acquisitions		4,841
Change in fair value of contingent consideration	145	(279)
Accretion of contingent consideration	1,030	568
Unrealized gain related to currency translation	28	61
Ending Balance	$ 3,890	$ 6,727
Minimum
Liabilities:
Discounted rate of cash outflow projections (as a percent)	14.50%
Incremental borrowing rate used to discount future cash flows from financial instruments (as a percent)	2.00%
Maximum
Liabilities:
Discounted rate of cash outflow projections (as a percent)	19.80%
Incremental borrowing rate used to discount future cash flows from financial instruments (as a percent)	4.83%
Level 3
Liabilities:
Fair value of outstanding borrowing	$ 118,000		124,900
Recurring
Assets:
Cash equivalents	1,548		22
Total	1,548		22
Liabilities:
Contingent consideration	3,890		6,073
Total	3,890
Recurring | Level 1
Assets:
Cash equivalents	1,548		22
Total	1,548		22
Recurring | Level 3
Liabilities:
Contingent consideration	3,890		$ 6,073
Total	$ 3,890