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Income taxes (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended
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Mar. 31, 2012 | Sep. 30, 2013
Income Tax Disclosure [Abstract] |  |
Income tax expense for unrecognized tax positions | $ 2.2 |
Reduction in deferred income tax expense due to deferred income tax rate reduction | 2.5 |
Unrecognized tax benefits to be settled within 12 months |  | $ 14.9
Anticipated settlement of federal and state audits |  | 12 months

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- Definition Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Unrecognized Tax Benefit -URI http://asc.fasb.org/extlink&oid=6527854 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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