SIGNIFICANT ACCOUNTING POLICIES - Purchased Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Purchased intangible assets
Weighted average amortization period	4 years
Gross	$ 57,731	$ 54,796
Accumulated Amortization	(54,066)	(48,916)
Net	3,665	5,880
Expected future amortization of intangible assets
2021	1,056
2022	875
2023	875
2024	859
Net	$ 3,665	5,880
Core technology
Purchased intangible assets
Weighted average amortization period	3 years 11 months 26 days
Gross	$ 17,899	17,717
Accumulated Amortization	(14,234)	(11,837)
Net	3,665	5,880
Expected future amortization of intangible assets
Net	3,665	5,880
Customer relationships
Purchased intangible assets
Gross	37,638	35,091
Accumulated Amortization	(37,638)	(35,091)
Net	0	0
Expected future amortization of intangible assets
Net	0	0
Trademarks / Trade names
Purchased intangible assets
Gross	2,194	1,988
Accumulated Amortization	(2,194)	(1,988)
Net	0	0
Expected future amortization of intangible assets
Net	$ 0	$ 0