SIGNIFICANT ACCOUNTING POLICIES - Purchased Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Purchased intangible assets
Weighted average amortization period	12 years
Gross	$ 58,069	$ 61,420
Accumulated Amortization	(49,480)	(48,559)
Net	8,589	12,861
Expected future amortization of intangible assets
2019	1,396
2020	1,396
2021	1,050
2022	823
2023	823
Thereafter	3,101
Net	$ 8,589	12,861
Core technology
Purchased intangible assets
Weighted average amortization period	20 years
Gross	$ 18,916	20,027
Accumulated Amortization	(10,866)	(10,333)
Net	8,050	9,694
Expected future amortization of intangible assets
Net	$ 8,050	9,694
Customer relationships
Purchased intangible assets
Weighted average amortization period	9 years
Gross	$ 37,122	39,244
Accumulated Amortization	(36,583)	(36,077)
Net	539	3,167
Expected future amortization of intangible assets
Net	$ 539	3,167
Trademarks / Trade names
Purchased intangible assets
Weighted average amortization period	9 years
Gross	$ 2,031	2,149
Accumulated Amortization	(2,031)	(2,149)
Net	0	0
Expected future amortization of intangible assets
Net	$ 0	$ 0