LEASES - Components of Lease Expense (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 13,979	$ 11,613
Sublease income	(2,834)	(2,732)
Net lease cost	$ 11,145	$ 8,881
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