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Income taxes (Details) (USD $) | 3 Months Ended
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Mar. 31, 2012 | Mar. 31, 2011
Income Tax Disclosure [Abstract] |  |
Income tax expense for unrecognized tax positions | $ 2,200,000 |
Reduction in deferred income tax expense due to deferred income tax rate reduction | 2,500,000 |
Income tax benefit from continuing operations |  | 4,200,000
Unrecognized tax benefits, decreases resulting from settlements with taxing authorities |  | 2,800,000
Interest related to reversal of unrecognized tax benefits previously established for 2004 through 2006 tax years |  | $ 600,000

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- Definition The gross amount of decreases in unrecognized tax benefits resulting from settlements with taxing authorities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Interpretation (FIN) -Number 48 -Paragraph 21 -Subparagraph a(3) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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. + Details
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