SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Restructuring Costs (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Restructuring Reserve [Roll Forward]
Charged to restructuring costs	$ 1,351			$ 724	$ 1,979	$ 724
Direct write off related to abandoned locations	400
Cost Optimization Project [Member] | On-Going Benefit Costs [Member]
Restructuring Reserve [Roll Forward]
Balance at January 1, 2018	433	$ 512	$ 87		87
Charged to restructuring costs	774	175	435
Payments	(251)	(254)	(10)
Balance at March 31, 2018	956	433	512		956
Cost Optimization Project [Member] | Exit Costs [Member]
Restructuring Reserve [Roll Forward]
Balance at January 1, 2018	346	387	441		441
Charged to restructuring costs	212	18	0
Payments	(41)	(59)	(54)
Balance at March 31, 2018	$ 517	$ 346	$ 387		$ 517