SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fair Value (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Change in the contingent consideration liability
Beginning Balance	$ 3,698	$ 6,073
Payment of contingent consideration	(2,401)	(3,245)
Accretion of contingent consideration	1,074	739
Unrealized gain related to currency translation	3	98
Ending Balance	2,374	$ 3,665
Outstanding borrowings	110,200		$ 116,700
Fair value of outstanding borrowing	$ 110,300		116,500
Minimum
Liabilities:
Discounted rate of cash outflow projections (as a percent)	14.50%
Change in the contingent consideration liability
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)	27.90%
Change in the contingent consideration liability
Incremental borrowing rate used to discount future cash flows from financial instruments (as a percent)	5.59%
Recurring
Assets:
Cash equivalents	$ 313		303
Total	313		303
Liabilities:
Contingent consideration	2,374		3,698
Total	2,374		3,698
Recurring | Level 1
Assets:
Cash equivalents	313		303
Total	313		303
Recurring | Level 3
Liabilities:
Contingent consideration	2,374		3,698
Total	$ 2,374		$ 3,698