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Equity method investments (Details) (USD $) In Millions, unless otherwise specified | Sep. 30, 2011 | Dec. 31, 2010 | Nov. 30, 2010 | Sep. 30, 2010
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Schedule of Equity Method Investments [Line Items] |  |  |  |
Ownership interest in ECTE sold (in hundredths) |  |  | 59.96% |
Total assets of equity method investments | $ 108.0 | $ 107.4 |  | $ 390.4
Total long-term debt of equity method investments | 39.7 | 30.1 |  | 152.6
Investment in equity method investments | 10.5 | 10.9 |  | 64.4
Undistributed earnings of equity method investments | $ 2.9 | $ 1.9 |  | $ 11.6

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