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Summary of significant accounting policies (Property and equipment) (Details) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2013 reporting_unit | Dec. 31, 2012 | Dec. 31, 2011
Property, Plant and Equipment [Line Items] |  |  |
Number of reporting units | 6 |  |
Estimated useful life, intangible assets | 14 years |  |
Impairment of intangible assets | $ 0 | $ 1,161,000 | $ 0
Minimum [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Estimated useful life, property and equipment | 3 years |  |
Estimated useful life, intangible assets | 3 years |  |
Maximum [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Estimated useful life, property and equipment | 20 years |  |
Estimated useful life, intangible assets | 17 years |  |
Rental Equipment [Member] | Minimum [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Estimated useful life, property and equipment | 3 years |  |
Rental Equipment [Member] | Maximum [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Estimated useful life, property and equipment | 10 years |  |
Intangible Assets, Amortization Period [Member] | Amortization Expense [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Change in accounting estimate, financial impact |  |  | 2,200,000
Intangible Assets, Amortization Period [Member] | Net Income [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Change in accounting estimate, financial impact |  |  | $ 1,400,000
Intangible Assets, Amortization Period [Member] | Earnings Per Share, Diluted [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Change in accounting estimate, financial impact (in dollars per share) |  |  | $ 0.03

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- Definition Change in Accounting Estimate, Financial Impact Per Share + References No definition available. + Details
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- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition The amount of impairment loss recognized in the period resulting from the write-down of the carrying amount of an intangible asset (excluding goodwill) to fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16373-109275 + Details
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- Details
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- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
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