Property plant and equipment (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 02, 2016	Jan. 03, 2015	Dec. 28, 2013
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 268,663	$ 200,142
Property, Plant and Equipment	176,513	112,492
Depreciation	16,100	13,600	$ 12,100
Capital Lease Costs [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	10,500	5,400
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	167,556	126,520
Property, Plant and Equipment	102,143	67,154
Inventory, Parts and Components, Net of Reserves	5,100	3,600
Machinery and Equipment [Member] | Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	12,100	9,800
Machinery and Equipment [Member] | Capital Lease Costs [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 12,200	$ 6,000