LEASES - Components of Lease Expense (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 8,843	$ 7,632
Sublease income	(2,044)	(1,685)
Net lease cost	$ 6,799	$ 5,947
Minimum
Lessee, Lease, Description [Line Items]
Remaining ​lease​ terms	1 year
Optional extension period	1 year
Maximum
Lessee, Lease, Description [Line Items]
Remaining ​lease​ terms	12 years
Optional extension period	5 years