Inventories - Summary of inventories (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Inventory Disclosure [Abstract]
Raw materials and common parts, net of reserve	$ 6,680us-gaap_InventoryRawMaterials	$ 6,832us-gaap_InventoryRawMaterials
Work-in-process, net of reserve	2,280us-gaap_InventoryWorkInProcess	2,380us-gaap_InventoryWorkInProcess
Finished goods, net of reserve	3,080us-gaap_InventoryFinishedGoods	2,717us-gaap_InventoryFinishedGoods
Total inventories	$ 12,040us-gaap_InventoryNet	$ 11,929us-gaap_InventoryNet

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Amount before valuation and LIFO reserves of completed merchandise or goods expected to be sold within one year or operating cycle, if longer.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 6

-Subparagraph a

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-Name Accounting Standards Codification

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-Subparagraph (SX 210.5-02.6(a)(1))

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Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-Section S99

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-Subparagraph (SX 210.5-02.6(a))

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-Publisher FASB

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Amount before valuation and LIFO reserves of raw materials expected to be sold, or consumed within one year or operating cycle, if longer.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 6

-Subparagraph a

-Article 5

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

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-Name Accounting Standards Codification

-Topic 210

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Amount before valuation and LIFO reserves of merchandise or goods in the production process expected to be completed within one year or operating cycle, if longer.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 6

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

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-Name Accounting Standards Codification

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