Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	Apr. 01, 2017	Dec. 31, 2016
Summary of Finite-lived intangible assets
Adjusted cost	$ 29,633	$ 29,307
Accumulated amortization	(29,272)	(28,895)
Finite lived intangible assets, Net carrying amount	361	412
Developed technology [Member]
Summary of Finite-lived intangible assets
Adjusted cost	16,026	15,726
Accumulated amortization	(15,715)	(15,380)
Finite lived intangible assets, Net carrying amount	311	346
Customer relationships [Member]
Summary of Finite-lived intangible assets
Adjusted cost	9,348	9,322
Accumulated amortization	(9,348)	(9,322)
Finite lived intangible assets, Net carrying amount	0	0
Brand names [Member]
Summary of Finite-lived intangible assets
Adjusted cost	1,927	1,927
Accumulated amortization	(1,927)	(1,927)
Finite lived intangible assets, Net carrying amount	0
Patented technology [Member]
Summary of Finite-lived intangible assets
Adjusted cost	2,252	2,252
Accumulated amortization	(2,202)	(2,186)
Finite lived intangible assets, Net carrying amount	50	66
Trademark [Member]
Summary of Finite-lived intangible assets
Adjusted cost	80	80
Accumulated amortization	(80)	(80)
Finite lived intangible assets, Net carrying amount	$ 0	$ 0