Equity method investments (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011	Dec. 31, 2010	Nov. 30, 2010	Sep. 30, 2010
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