SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Restructuring Costs (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Restructuring Reserve [Roll Forward]
Charged to restructuring costs	$ 2,330		$ 137	$ 2,894	$ 1,277
Restructuring costs	2,330		$ 137	2,894	$ 1,277
Employee Termination Costs | 2019 Restructuring Plan
Restructuring Reserve [Roll Forward]
Beginning balance	306	$ 386		386
Charged to restructuring costs	1,565	212
Payments	(1,096)	(292)
Ending balance	775	306		775
Restructuring costs	1,565	212
Lease-Related Exit Costs | 2019 Restructuring Plan
Restructuring Reserve [Roll Forward]
Beginning balance	1,167	1,223		1,223
Charged to restructuring costs	535	20
Payments	(170)	(76)
Ending balance	1,532	1,167		1,532
Restructuring costs	$ 535	$ 20
Legal Entity Reorganization
Restructuring Reserve [Roll Forward]
Charged to restructuring costs				200
Restructuring costs				200
Strategic Reduction of Real Estate Footprint
Restructuring Reserve [Roll Forward]
Charged to restructuring costs				300
Restructuring costs				300
Other Restructuring Costs
Restructuring Reserve [Roll Forward]
Charged to restructuring costs				100
Restructuring costs				$ 100