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Income taxes - Reconciliation of unrecognized tax benefits (Details) - USD ($) $ in Millions | Mar. 31, 2021 | Dec. 31, 2020 | Mar. 31, 2020
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Income Tax Disclosure |  |  |
Beginning Balance | $ 14.8 | $ 16.3 | $ 16.3
Ending Balance | $ 14.8 | $ 14.8 | $ 16.3

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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 10B -URI http://asc.fasb.org/extlink&oid=120406818&loc=SL37586934-109318 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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