Current Liabilities - Deferred Services Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 04, 2015	Jun. 28, 2014	Jul. 04, 2015	Jun. 28, 2014	Apr. 04, 2015	Dec. 31, 2014	Mar. 29, 2014
Balance sheets classification
Deferred service income-short term	$ 7,700		$ 7,700			$ 9,800
Deferred service income-long term	329		329			$ 1,051
Service Contracts
Balance sheets classification
Deferred service income-short term					$ 4,438		$ 3,620
Deferred service income-long term					$ 329		$ 592
Movement in Deferred Revenue [Roll Forward]
Balance, beginning of the period	5,249	$ 4,778	5,233	$ 5,499
Additions	877	415	2,223	988
Revenue recognized	(1,359)	(981)	(2,689)	(2,275)
Balance, end of the period	$ 4,767	$ 4,212	$ 4,767	$ 4,212