SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Restructuring Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Restructuring Reserve [Roll Forward]
Charged to restructuring costs	$ 435	$ 0
Cost Optimization Project [Member] | On-Going Benefit Costs [Member]
Restructuring Reserve [Roll Forward]
Balance at beginning of period	87
Charged to restructuring costs	435
Payments	(10)
Balance at end of period	512
Cost Optimization Project [Member] | Exit Costs [Member]
Restructuring Reserve [Roll Forward]
Balance at beginning of period	441
Charged to restructuring costs	0
Payments	(54)
Balance at end of period	$ 387