The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Goodwill and other intangible assets (Details Textual) - USD ($)	12 Months Ended
	Jan. 02, 2016	Dec. 27, 2014	Dec. 28, 2013
Business Acquisition [Line Items]
Impairment of Intangible Assets, Finite-lived			$ 1,800,000
Goodwill, Impairment Loss			200,000
Goodwill	$ 48,751,000	$ 48,751,000
Amortization expense related to acquisition of intangible assets	3,500,000	$ 3,500,000	$ 3,800,000
Goodwill, Impaired, Accumulated Impairment Loss	200,000
Evolution Robotics, Inc. (ER) [Member]
Business Acquisition [Line Items]
Goodwill	41,000,000
Nekton Research LLC [Member]
Business Acquisition [Line Items]
Goodwill	7,709,000
Goodwill, Gross	$ 7,900,000
Minimum [Member]
Business Acquisition [Line Items]
Estimated useful lives for intangible assets	2 years
Maximum [Member]
Business Acquisition [Line Items]
Estimated useful lives for intangible assets	10 years
Defense & Security Robots [Member] \| Nekton Research LLC [Member]
Business Acquisition [Line Items]
Goodwill, Gross	$ 7,700,000
Research Reporting Unit [Member] \| Nekton Research LLC [Member]
Business Acquisition [Line Items]
Goodwill, Gross	$ 200,000