Purchased Intangible Assets - (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Finite-lived intangibles, Gross Carrying Amount	$ 79,848	$ 79,748
Finite-lived intangibles, Accumulated Amortization	71,496	71,116
Finite-lived intangibles, Net	8,352	8,632
Developed Technology [Member]
Finite Lived Intangible Assets [Line Items]
Finite-lived intangibles, Gross Carrying Amount	65,927	65,827
Finite-lived intangibles, Accumulated Amortization	58,812	58,522
Finite-lived intangibles, Net	7,115	7,305
Customer and Distributor Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Finite-lived intangibles, Gross Carrying Amount	9,560	9,560
Finite-lived intangibles, Accumulated Amortization	8,883	8,818
Finite-lived intangibles, Net	677	742
Trade Names [Member]
Finite Lived Intangible Assets [Line Items]
Finite-lived intangibles, Gross Carrying Amount	4,361	4,361
Finite-lived intangibles, Accumulated Amortization	3,801	3,776
Finite-lived intangibles, Net	$ 560	$ 585