LEASES - Operating Lease Arrangements (Details) $ in Thousands	1 Months Ended
	Mar. 31, 2018 USD ($) ft² item $ / ft²	Jan. 31, 2016 ft²	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 ft²	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Operating lease liabilities | $			$ 9,495
CMO
Lessee, Lease, Description [Line Items]
Square of feet of space | ft²		3,267
Term of lease extension option		2 years
Advance written notice termination period		2 years
Vehicle leases
Lessee, Lease, Description [Line Items]
Lease term						12 months
Stoughton, Massachusetts
Lessee, Lease, Description [Line Items]
Square of feet of space | ft²	50,678
Rent-free term	4 months
Lease term	10 years
Number of renewal periods | item	2
Term of lease extension option	5 years
Base rent | $	$ 1,214
Annual base rent per rentable square foot | $ / ft²	23.95
Canton, Massachusetts
Lessee, Lease, Description [Line Items]
Square of feet of space | ft²					9,660
Operating lease liabilities | $				$ 0
Maximum | Stoughton, Massachusetts
Lessee, Lease, Description [Line Items]
Increase in annual base rent	3.10%
Minimum | Stoughton, Massachusetts
Lessee, Lease, Description [Line Items]
Increase in annual base rent	2.50%