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Income taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	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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Anticipated settlement of federal and state audits.

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- Definition

Income tax expense for tax positions unrecognized.

+ References

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- Definition

Reduction in deferred income tax expense due to deferred income tax rate reduction.

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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

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