SIGNIFICANT ACCOUNTING POLICIES - Purchased Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Purchased intangible assets
Weighted average amortization period	12 years
Gross	$ 61,420	$ 55,742
Accumulated Amortization	(48,559)	(39,915)
Net	12,861	15,827
Expected future amortization of intangible assets
2018	2,984
2019	1,669
2020	1,669
2021	1,304
2022	1,067
Thereafter	4,168
Net	$ 12,861	15,827
Core technology
Purchased intangible assets
Weighted average amortization period	20 years
Gross	$ 20,027	17,751
Accumulated Amortization	(10,333)	(8,165)
Net	9,694	9,586
Expected future amortization of intangible assets
Net	$ 9,694	9,586
Customer relationships
Purchased intangible assets
Weighted average amortization period	9 years
Gross	$ 39,244	36,088
Accumulated Amortization	(36,077)	(29,965)
Net	3,167	6,123
Expected future amortization of intangible assets
Net	$ 3,167	6,123
Trademarks / Trade names
Purchased intangible assets
Weighted average amortization period	9 years
Gross	$ 2,149	1,903
Accumulated Amortization	(2,149)	(1,785)
Net	0	118
Expected future amortization of intangible assets
Net	$ 0	$ 118