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Summary of Significant Accounting Policies, Textuals (Details) (USD $) In Millions, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014
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Significant accounting policies |  |
Percentage of Employees Covered by Collective Bargaining Agreements | 100.00%kalu_PercentageofEmployeesCoveredbyCollectiveBargainingAgreements |
Percentage of Employees Covered by Collective Bargaining Agreements Expiring Within One Year | 0.00%kalu_PercentageofEmployeesCoveredbyCollectiveBargainingAgreementsExpiringWithinOneYear |
Fabricated Products |  |
Significant accounting policies |  |
Excess of current cost over the stated LIFO value of inventory | $ 24.7 us-gaap_InventoryLIFOReserve / us-gaap_StatementBusinessSegmentsAxis = kalu_FabricatedProductsMember | $ 37.6 us-gaap_InventoryLIFOReserve / us-gaap_StatementBusinessSegmentsAxis = kalu_FabricatedProductsMember

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- Definition Percentage of Employees Covered by Collective Bargaining Agreements + References No definition available. + Details
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- Definition Percentage of Employees Covered by Collective Bargaining Agreements Expiring Within One Year + References No definition available. + Details
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- Details
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- Definition Amount of difference between inventory at lower of LIFO cost or market and inventory at lower of other inventory accounting method cost or market, for example, but not limited to, FIFO or average cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6(c)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Details
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