Income taxes (Components of deferred income tax valuation allowance) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Income Tax Disclosure [Abstract]
Valuation Allowance, Amount	$ 9,090	$ 9,347
Income Tax Reconciliation, Change in Deferred Tax Assets Valuation Allowance	72	(267)	$ 4,015
Valuation Allowance Deferred Tax Asset Change Due To Acquisition FX	0	10
Valuation Allowance, Amount	$ 9,162	$ 9,090	$ 9,347

Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in the valuation allowance for deferred tax assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e32123-109318

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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