Research and development (Details) (USD $) In Thousands, unless otherwise specified	0 Months Ended	3 Months Ended
Jul. 31, 2013	Jan. 03, 2015	Dec. 28, 2013
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense, net of grants receivable		$ 1,234us-gaap_ResearchAndDevelopmentExpense	$ 930us-gaap_ResearchAndDevelopmentExpense
Percentage of sales (in hundredths)		12.40%sev_PercentageOfSales	10.30%sev_PercentageOfSales
Cummins Generator Technologies and Newcastle University [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Grant income recorded		8	17
Research and development expense on projects		23	50
Low Emission Transport Collaborative Projects Fund [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Grant income recorded		16	97
Research and development expense on projects		66	422
Total grants awarded	$ 480

Research and development percentage of sales.

No definition available.

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- Definition

Total grants awarded under a research and development arrangement accounted for as a contract to perform research and development for others.

+ References

No definition available.

+ Details

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- Definition

The amount of compensation earned (contract income) under a research and development arrangement accounted for as a contract to perform research and development for others.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 730

-SubTopic 20

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6420387&loc=d3e23221-108380

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 730

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6420387&loc=d3e23199-108380

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- Definition

The amount of costs incurred under a research and development arrangement accounted for as a contract to perform research and development for others.

+ References

+ Details

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- Definition

The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 985

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 730

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373

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