Stockholders' Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified
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12 Months Ended |
3 Months Ended |
Dec. 31, 2014
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Dec. 31, 2013
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Dec. 31, 2012
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Mar. 31, 2015
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Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract] |
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Preferred stock, issued |
0us-gaap_PreferredStockSharesIssued |
0us-gaap_PreferredStockSharesIssued |
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Share-based Compensation Arrangement by Share-based Payment Award, Additional General Disclosures [Abstract] |
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Number of share-based compensation plans |
2ati_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofPlans |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Granted (shares) |
675,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod |
576,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod |
394,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod |
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Common stock shares available for future awards |
1,600,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant |
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Shares vested |
18,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod |
333,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod |
343,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod |
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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |
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Nonvested beginning of the year (shares) |
927,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber |
727,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber |
677,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber |
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Granted (shares) |
675,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod |
576,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod |
394,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod |
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Vested (shares) |
(18,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod |
(333,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod |
(343,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod |
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Forfeited (shares) |
(208,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod |
(43,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod |
(1,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod |
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Nonvested end of the year (shares) |
1,376,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber |
927,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber |
727,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber |
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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward] |
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Beginning balance (in dollars per share) |
$ 36.9us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue |
$ 38.6us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue |
$ 36.4us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue |
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Granted (in dollars per share) |
$ 20.3us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue |
$ 16.4us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue |
$ 16.4us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue |
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Vested (in dollars per share) |
$ (1.0)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue |
$ (16.4)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue |
$ (14.1)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue |
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Forfeited (in dollars per share) |
$ (8.4)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue |
$ (1.7)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue |
$ (0.1)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue |
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Ending balance (in dollars per share) |
$ 47.8us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue |
$ 36.9us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue |
$ 38.6us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue |
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Retained Earnings Note Disclosure [Abstract] |
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Undistributed earnings of investees accounted for under equity method |
$ 12ati_RetainedEarningsEquityMethodUndistributedEarnings |
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Restricted Stock [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Income target attainment measurement period |
3 years |
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Share based compensation expense |
2.4us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember |
11.3us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember |
14.0us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember |
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Unrecognized compensation expense |
18.9us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember |
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Performance Awards [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Unrecognized compensation expense |
10.3us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember |
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TSR/TSRP Minimum Shares |
0ati_TsrpMinimumShares / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember |
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TSR/TSRP Target Shares |
789,000ati_TsrpTargetShares / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember |
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TSR/TSRP Maximum Shares |
1,580,000ati_TsrpMaximumShares / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember |
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PRSP 2014 [Member] | Restricted Stock [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Granted (shares) |
492,773us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ati_PRSP2014Member |
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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |
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Granted (shares) |
492,773us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ati_PRSP2014Member |
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LTSV 2014 [Member] | Restricted Stock [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Granted (shares) |
113,827us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ati_LongTermShareholderValueLTSV2014Member |
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Award vesting period |
3 years |
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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |
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Granted (shares) |
113,827us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ati_LongTermShareholderValueLTSV2014Member |
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PRSP 2012 [Member] | Restricted Stock [Member] |
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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |
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Forfeited (shares) |
(171,083)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ati_PRSP2012Member |
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TSRP 2012-2014 [Member] | Performance Awards [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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TSR/TSRP Award Fair Value |
8.8ati_TsrpAwardFairValue / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_Tsrp20122014Member |
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Unrecognized compensation expense |
0us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_Tsrp20122014Member |
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TSR/TSRP Minimum Shares |
0ati_TsrpMinimumShares / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_Tsrp20122014Member |
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TSR/TSRP Target Shares |
186,000ati_TsrpTargetShares / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_Tsrp20122014Member |
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TSR/TSRP Maximum Shares |
373,000ati_TsrpMaximumShares / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_Tsrp20122014Member |
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TSRP 2013-2015 [Member] | Performance Awards [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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TSR/TSRP Award Fair Value |
11.0ati_TsrpAwardFairValue / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSRP20132015MemberMember |
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Unrecognized compensation expense |
3.7us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSRP20132015MemberMember |
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TSR/TSRP Minimum Shares |
0ati_TsrpMinimumShares / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSRP20132015MemberMember |
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TSR/TSRP Target Shares |
309,000ati_TsrpTargetShares / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSRP20132015MemberMember |
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TSR/TSRP Maximum Shares |
618,000ati_TsrpMaximumShares / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSRP20132015MemberMember |
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TSR 2014-2016 [Member] | Performance Awards [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Target share award level |
319,955ati_TargetShareAwardLevel / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSR20142016Member |
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TSR/TSRP Award Fair Value |
9.9ati_TsrpAwardFairValue / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSR20142016Member |
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Unrecognized compensation expense |
6.6us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSR20142016Member |
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TSR/TSRP Minimum Shares |
0ati_TsrpMinimumShares / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSR20142016Member |
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TSR/TSRP Target Shares |
294,000ati_TsrpTargetShares / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSR20142016Member |
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TSR/TSRP Maximum Shares |
589,000ati_TsrpMaximumShares / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSR20142016Member |
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TSR and TSRP Awards [Member] | Performance Awards [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Share based compensation expense |
$ 9.8us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSRandTSRPAwardsMember |
$ 12.3us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSRandTSRPAwardsMember |
$ 19.2us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSRandTSRPAwardsMember |
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Performance measurement period |
3 years |
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Common stock shares available for future awards |
1,850,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSRandTSRPAwardsMember |
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Maximum [Member] | Restricted Stock [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Award vesting period |
5 years |
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Maximum [Member] | PRSP 2013 [Member] | Restricted Stock [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Award vesting period |
5 years |
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Maximum [Member] | TSR and TSRP Awards [Member] | Performance Awards [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Award multiplier |
2ati_ShareBasedCompensationArrangementbySharebasedPaymentAwardAwardMultiplier / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSRandTSRPAwardsMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
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Minimum [Member] | Restricted Stock [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Award vesting period |
3 years |
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Minimum [Member] | PRSP 2014 [Member] | Restricted Stock [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Award vesting period |
3 years |
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Minimum [Member] | TSR and TSRP Awards [Member] | Performance Awards [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Award multiplier |
0ati_ShareBasedCompensationArrangementbySharebasedPaymentAwardAwardMultiplier / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_TSRandTSRPAwardsMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
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Subsequent Event [Member] | TSRP 2012-2014 [Member] | Performance Awards [Member] |
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Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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Shares vested |
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137,843us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_Tsrp20122014Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |
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Vested (shares) |
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(137,843)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = ati_Tsrp20122014Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |