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Commitments, Guarantees and Contingencies - Leasing Agreements (Details) (USD $) In Millions, unless otherwise specified | Mar. 31, 2015
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Leasing Agreements [Line Items] |
Operating Leases, Minimum Payments Due in 2015 | $ 13.4 us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent
Operating Leases, Minimum Payments Due in 2016 | 11.4 us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears
Operating Leases, Minimum Payments Due in 2017 | 10.6 us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears
Operating Leases, Minimum Payments Due in 2018 | 9.5 us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears
Operating Leases, Minimum Payments Due in 2019 | 8.3 us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears
Operating Leases, Minimum Payments Due Thereafter | 27.3 us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter
BNI Coal Dragline Lease [Member] |
Leasing Agreements [Line Items] |
Operating Leases, Minimum Payments Due in 2015 | 2.8 us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_ExplorationAndProductionEquipmentMember
Termination Fee | 3.0 ale_TerminationFee / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_ExplorationAndProductionEquipmentMember
Operating Leases, Minimum Payments Due in 2016 | 2.8 us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_ExplorationAndProductionEquipmentMember
Operating Leases, Minimum Payments Due in 2017 | 2.8 us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_ExplorationAndProductionEquipmentMember
Operating Leases, Minimum Payments Due in 2018 | 2.8 us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_ExplorationAndProductionEquipmentMember
Operating Leases, Minimum Payments Due in 2019 | 2.8 us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_ExplorationAndProductionEquipmentMember
Operating Leases, Minimum Payments Due Thereafter | $ 22.4 us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter / us-gaap_PropertyPlantAndEquipmentByTypeAxis = us-gaap_ExplorationAndProductionEquipmentMember

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- Definition A lump sum payment in conjunction with a lease termination. + References No definition available. + Details
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- Details
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- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: 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 Reference 2: 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 + Details
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X
- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: 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 Reference 2: 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 + Details
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- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: 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 Reference 2: 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 + Details
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- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: 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 Reference 2: 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 + Details
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- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: 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 Reference 2: 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 + Details
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- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: 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 Reference 2: 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 + Details
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