Quarterly report pursuant to Section 13 or 15(d)

NET INCOME (LOSS) PER SHARE (Narrative) (Details)

v2.4.1.9
NET INCOME (LOSS) PER SHARE (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Apr. 24, 2014
Stock options          
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]          
Antidilutive securities excluded from computation of earnings per share 1.8us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
11.5us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
2.6us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
13.8us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
 
Restricted stock          
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]          
Antidilutive securities excluded from computation of earnings per share 0.1us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
11.5us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
0.1us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
10.7us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
 
4.50% convertible subordinated notes          
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]          
Antidilutive securities excluded from computation of earnings per share    42.5us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedFourAndHalfPercentNotesMember
42.5us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedFourAndHalfPercentNotesMember
42.5us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedFourAndHalfPercentNotesMember
 
Interest per annum on the principal amount 4.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedFourAndHalfPercentNotesMember
  4.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedFourAndHalfPercentNotesMember
   
Antidilutive income excluded from computation of earnings per share   $ 0.9qtm_AntidilutiveIncomeExcludedFromComputationOfEarningsPerShare
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedFourAndHalfPercentNotesMember
$ 2.7qtm_AntidilutiveIncomeExcludedFromComputationOfEarningsPerShare
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedFourAndHalfPercentNotesMember
$ 2.7qtm_AntidilutiveIncomeExcludedFromComputationOfEarningsPerShare
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedFourAndHalfPercentNotesMember
 
3.50% convertible subordinated notes          
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]          
Antidilutive securities excluded from computation of earnings per share 30.9us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember
31.2us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember
30.9us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember
31.2us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember
 
Interest per annum on the principal amount 3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember
3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember
3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember
3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember
3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember
Antidilutive income excluded from computation of earnings per share $ 1.4qtm_AntidilutiveIncomeExcludedFromComputationOfEarningsPerShare
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember
$ 1.4qtm_AntidilutiveIncomeExcludedFromComputationOfEarningsPerShare
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember
$ 4.3qtm_AntidilutiveIncomeExcludedFromComputationOfEarningsPerShare
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember
$ 4.3qtm_AntidilutiveIncomeExcludedFromComputationOfEarningsPerShare
/ us-gaap_DebtInstrumentAxis
= qtm_ConvertibleSubordinatedThreeAndHalfPercentNotesMember