Commitments and Contingencies (Details) (USD $) In Millions	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2011
Commitments and Contingencies (Textuals) [Abstract]
Minimum rental commitments under operating lease, one year	$ 7.8	$ 7.8
Minimum rental commitments under operating lease, second year	6.9	6.9
Minimum rental commitments under operating lease, third year	6.0	6.0
Minimum rental commitments under operating lease, fourth year	3.5	3.5
Minimum rental commitments under operating lease, five year	2.9	2.9
Operating Leases, Future Minimum Payments Due, Total	35.2	35.2
Expected period related to remediation plans for environmental contingencies		30 years
Increase in environmental accrual	2.5
Potential increase in environemental costs	21.6	21.6
Environmental accrual	21.8	21.8
Expenditures to be charged to environmental accruals, one year	0.5	0.5
Expenditures to be charged to environmental accruals, second year	1.0	1.0
Expenditures to be charged to environmental accruals, third year	4.0	4.0
Expenditures to be charged to environmental accruals, fourth year	0.8	0.8
Expenditures to be charged to environmental accruals, fifth year	0.8	0.8
Expenditures to be charged to environmental accruals, after 2015	$ 14.7	$ 14.7
Expected period related to environmental contingency payments in excess of current accruals		30 years
Time period within which Company's recorded estimate of its obligation may change		12 months

Commitments and Contingencies Textuals Abstract.

Name:	kalu_CommitmentsAndContingenciesTextualsAbstract
Namespace Prefix:	kalu
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Expected period related to environmental contingency payments in excess of current.

+ Details

Name:	kalu_ExpectedPeriodRelatedToEnvironmentalContingencyPaymentsInExcessOfCurrentAccruals
Namespace Prefix:	kalu
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Expected Period Related to Remediation Plans for Environmental Contingencies.

+ Details

Name:	kalu_ExpectedPeriodRelatedToRemediationPlansForEnvironmentalContingencies
Namespace Prefix:	kalu
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Potential additional environmental costs.

+ Details

Name:	kalu_PotentialAdditionalEnvironmentalCosts
Namespace Prefix:	kalu
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Time period within which Company's recorded estimate of its obligation may change.

+ Details

Name:	kalu_TimePeriodWithinWhichCompanysRecordedEstimateOfItsObligationMayChange
Namespace Prefix:	kalu
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Total costs accrued as of the balance sheet date for environmental loss contingencies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 25
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 96-1
-Paragraph 161
-Subparagraph a
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 5
-Paragraph 9
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6952336&loc=d3e14326-108349

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingencies
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Increase (decrease) in the accrual for environmental loss contingencies during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 5.Y.Q2)
-URI http://asc.fasb.org/extlink&oid=6572457&loc=d3e149879-122751

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesPeriodIncreaseDecrease
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

The portion of the estimated aggregate undiscounted amount of the accrual for environmental loss contingencies that is expected to be paid after the fifth year after the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 5
-Section Y
-Paragraph Question 1

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 5.Y.Q1)
-URI http://asc.fasb.org/extlink&oid=6572457&loc=d3e149879-122751

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueAfterFifthYear
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The portion of the estimated aggregate undiscounted amount of the accrual for environmental loss contingencies that is expected to be paid in the fifth year after the balance sheet date.

+ References

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInFifthYear
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The portion of the estimated aggregate undiscounted amount of the accrual for environmental loss contingencies that is expected to be paid in the fourth year after the balance sheet date.

+ References

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInFourthYear
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The portion of the estimated aggregate undiscounted amount of the accrual for environmental loss contingencies that is expected to be paid in the second year after the balance sheet date.

+ References

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInSecondYear
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The portion of the estimated aggregate undiscounted amount of the accrual for environmental loss contingencies that is expected to be paid in the third year after the balance sheet date.

+ References

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInThirdYear
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The portion of the estimated aggregate undiscounted amount of the accrual for environmental loss contingencies that is expected to be paid within one year of the balance sheet date.

+ References

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueWithinOneYear
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For leases having an initial or remaining non-cancelable letter-terms in excess of one year, required rental payments due within one year of the balance sheet date relating to leases defined as operating.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 13
-Paragraph 122
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 13
-Paragraph 16
-Subparagraph b(i)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 10
-Section 55
-Paragraph 40
-Subparagraph (Note 3)
-URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For leases having an initial or remaining non-cancelable letter-terms in excess of one year, required rental payments due within the fifth year of the balance sheet date relating to leases defined as operating.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For leases having an initial or remaining non-cancelable letter-terms in excess of one year, required rental payments due within the fourth year of the balance sheet date relating to leases defined as operating.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For leases having an initial or remaining non-cancelable letter-terms in excess of one year, required rental payments due within the third year of the balance sheet date relating to leases defined as operating.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For leases having an initial or remaining non-cancelable letter-terms in excess of one year, required rental payments due within the second year of the balance sheet date relating to leases defined as operating.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For leases having an initial or remaining non-cancelable letter-terms in excess of one year, required rental payments due after the fifth year from the balance sheet date on leases defined as operating.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant