| **Investments in and advances to non-consolidated affiliates (Narrative) (Details)** | Apr. 30, 2012Minimum [Member] | Apr. 30, 2012Maximum [Member] | Sep. 30, 2011NC2 Global, LLC [Member] | Aug. 31, 2011NC2 Global, LLC [Member] |
|--------------------------------------------------------------------------------------|-------------------------------|-------------------------------|---------------------------------------|---------------------------------------|
| **Schedule of Equity Method Investments [Line Items]**                               |                          |                          |                                  |                                  |
| Equity Method Investment, Ownership Percentage                                       | 10.00%                        | 50.00%                        | 100.00%                               | 50.00%                                |

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| - Definition
The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 159 -Paragraph 18 -Subparagraph f -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 18 -Paragraph 20 -Subparagraph a (1) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571
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| X                                                                                                                                                                              |
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