LEASES - Components of Lease Expense and Payments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
LEASES
Operating lease cost	$ 4,248	$ 4,029	$ 8,473	$ 8,076
Short-term lease cost	729	729	1,137	1,271
Variable lease cost	1,016	1,540	2,080	2,343
Total operating lease cost	5,993	6,298	11,690	11,690
Payments for lease liabilities			7,600	7,200
Lease liabilities arising from ROU			6,300	1,700
Finance lease cost:
Amortization of right-of-use asset	615	522	1,190	1,094
Variable costs	197	186	392	458
Total finance lease cost	812	$ 708	1,582	$ 1,552
Finance leases cost included in property, plant and equipment	26,700		26,700		$ 25,400
Accumulated amortization related to finance leases	10,700		10,700		9,500
Principal payments, finance lease liabilities			500
Additional finance lease liabilities recognized			1,400
Total	2,126		2,126		$ 1,129
Finance lease liability, current	$ 400		$ 400