SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Restructuring Costs (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Restructuring Reserve [Roll Forward]
Charged to restructuring costs	$ 193		$ 0	$ 628	$ 0
Cost Optimization Project [Member] | On-Going Benefit Costs [Member]
Restructuring Reserve [Roll Forward]
Balance at January 1, 2018	512	$ 87		87
Charged to restructuring costs	175	435
Payments	(254)	(10)
Balance at March 31, 2018	433	512		433
Cost Optimization Project [Member] | Exit Costs [Member]
Restructuring Reserve [Roll Forward]
Balance at January 1, 2018	387	441		441
Charged to restructuring costs	18	0
Payments	(59)	(54)
Balance at March 31, 2018	$ 346	$ 387		$ 346