Goodwill and Purchased Intangible Assets - Schedule of Purchased Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite Lived Intangible Assets [Line Items]
Finite-lived intangibles, Gross Carrying Amount	$ 79,748	$ 79,448
Finite-lived intangibles, Accumulated Amortization	71,116	69,175
Finite-lived intangibles, Net	8,632	10,273
Developed Technology [Member]
Finite Lived Intangible Assets [Line Items]
Finite-lived intangibles, Gross Carrying Amount	65,827	65,527
Finite-lived intangibles, Accumulated Amortization	58,522	56,986
Finite-lived intangibles, Net	7,305	8,541
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	8,818	8,514
Finite-lived intangibles, Net	742	1,046
Trade Names [Member]
Finite Lived Intangible Assets [Line Items]
Finite-lived intangibles, Gross Carrying Amount	4,361	4,361
Finite-lived intangibles, Accumulated Amortization	3,776	3,675
Finite-lived intangibles, Net	$ 585	$ 686