SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Restructuring Costs (Details) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
	Jan. 01, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Restructuring Reserve [Roll Forward]
Charged to restructuring costs		$ 1,607			$ 1,351	$ 2,884	$ 1,979
Cost Optimization Project [Member] | Lease-Related Exit Costs [Member]
Restructuring Cost and Reserve [Line Items]
ASC 842 lease reclassification	$ 300
2019 Restructuring Plan [Member] | Employee Termination Costs [Member]
Restructuring Reserve [Roll Forward]
Beginning balance	556	832	$ 1,287	$ 556		556
Charged to restructuring costs		238	137	1,104
Payments		(615)	(592)	(373)
Ending balance		455	832	1,287		455
2019 Restructuring Plan [Member] | Lease-Related Exit Costs [Member]
Restructuring Reserve [Roll Forward]
Beginning balance	$ 127	43	65	127		127
Charged to restructuring costs		1,310	0	0
Payments		(75)	(22)	(62)
Ending balance		$ 1,278	$ 43	$ 65		$ 1,278