Business combinations (Schedule of the Valuation of the Intangible Assets Acquired) (Details) - Ascend Management Innovations LLC $ in Thousands  | 
3 Months Ended | 
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 Dec. 31, 2016  
USD ($) 
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| Business Acquisition [Line Items] | |
| Finite-lived intangible assets acquired | $ 22,300 | 
| Customer relationships | |
| Business Acquisition [Line Items] | |
| Finite-lived intangible asset, useful life | 19 years | 
| Finite-lived intangible assets acquired | $ 20,400 | 
| Trade Names | |
| Business Acquisition [Line Items] | |
| Finite-lived intangible asset, useful life | 8 years | 
| Finite-lived intangible assets acquired | $ 1,700 | 
| Technology-Based Intangible Assets | |
| Business Acquisition [Line Items] | |
| Finite-lived intangible asset, useful life | 1 year | 
| Finite-lived intangible assets acquired | $ 200 | 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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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. No definition available. 
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- Definition Amount of increase in assets, excluding financial assets, lacking physical substance with a definite life, from an acquisition. No definition available. 
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