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Income Tax Matters, NOL (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Income Tax Disclosure [Abstract] |  |  |
Net operating loss carryforwards | $ 606.1 us-gaap_OperatingLossCarryforwards |  |
NOL carryforwards related to the excess tax benefits from vesting of employee restricted stock | 1.7 kalu_ExcessTaxBenefitFromEmployeeRestrictedStockResultingInNetOperatingLossCarryForwards |  |
AMT credit carryforwards | 30.1 us-gaap_TaxCreditCarryforwardAmount |  |
Increase (Decrease) in valuation allowance | $ (0.7)us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount | $ 1.2 us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount | $ (0.1)us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount

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- Definition Excess Tax Benefit From Employee Restricted Stock Resulting In Net Operating Loss Carry forwards. + References No definition available. + Details
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- Details
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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 + Details
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- Definition The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Carryforwards -URI http://asc.fasb.org/extlink&oid=6506874 + Details
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- Definition Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=37586315&loc=d3e32123-109318 + Details
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