2.2.0.25truefalse0130 - Statement - Consolidated Statements of Shareholders' EquitytruefalseIn Thousandsfalse1falsefalseUSDtruefalse{us-gaap_StatementEquityComponentsAxis} : Common Stock 4/1/2010 - 3/31/2011 USD ($) $TwelveMonthsEnded_31Mar2011_Common_Stock_Memberhttp://www.sec.gov/CIK0000874663na0001-01-01T00:00:000001-01-01T00:00:00falsefalseus-gaap_CommonStockMemberus-gaap_StatementEquityComponentsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_CommonStockMemberus-gaap_StatementEquityComponentsAxisexplicitMemberSharesStandardhttp://www.xbrl.org/2003/instancesharesxbrli0USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2falsefalseUSDtruefalse{us-gaap_StatementEquityComponentsAxis} : Non-voting Common Stock 3/31/2011 USD ($) $BalanceAsOf_31Mar2011_Nonvoting_Common_Stock_Memberhttp://www.sec.gov/CIK0000874663na0001-01-01T00:00:000001-01-01T00:00:00falsefalseus-gaap_NonvotingCommonStockMemberus-gaap_StatementEquityComponentsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_NonvotingCommonStockMemberus-gaap_StatementEquityComponentsAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170SharesStandardhttp://www.xbrl.org/2003/instancesharesxbrli0USDUSD$3falsefalseUSDtruefalse{us-gaap_StatementEquityComponentsAxis} : Additional Paid-in Capital [Member] 4/1/2010 - 3/31/2011 USD ($) $TwelveMonthsEnded_31Mar2011_Additional_Paid_In_Capital_Memberhttp://www.sec.gov/CIK0000874663na0001-01-01T00:00:000001-01-01T00:00:00falsefalseus-gaap_AdditionalPaidInCapitalMemberus-gaap_StatementEquityComponentsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_AdditionalPaidInCapitalMemberus-gaap_StatementEquityComponentsAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$4falsefalseUSDtruefalse{us-gaap_StatementEquityComponentsAxis} : Treasury Stock [Member] 4/1/2010 - 3/31/2011 USD ($) $TwelveMonthsEnded_31Mar2011_Treasury_Stock_Memberhttp://www.sec.gov/CIK0000874663na0001-01-01T00:00:000001-01-01T00:00:00falsefalseus-gaap_TreasuryStockMemberus-gaap_StatementEquityComponentsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_TreasuryStockMemberus-gaap_StatementEquityComponentsAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170SharesStandardhttp://www.xbrl.org/2003/instancesharesxbrli0USDUSD$5falsefalseUSDtruefalse{us-gaap_StatementEquityComponentsAxis} : Retained Earnings [Member] 4/1/2010 - 3/31/2011 USD ($) $TwelveMonthsEnded_31Mar2011_Retained_Earnings_Memberhttp://www.sec.gov/CIK0000874663na0001-01-01T00:00:000001-01-01T00:00:00falsefalseus-gaap_RetainedEarningsMemberus-gaap_StatementEquityComponentsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_RetainedEarningsMemberus-gaap_StatementEquityComponentsAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$6falsefalseUSDtruefalse{us-gaap_StatementEquityComponentsAxis} : Accumulated Translation Adjustment [Member] 3/31/2011 USD ($) $BalanceAsOf_31Mar2011_Accumulated_Translation_Adjustment_Memberhttp://www.sec.gov/CIK0000874663na0001-01-01T00:00:000001-01-01T00:00:00falsefalseus-gaap_AccumulatedTranslationAdjustmentMemberus-gaap_StatementEquityComponentsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_AccumulatedTranslationAdjustmentMemberus-gaap_StatementEquityComponentsAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$7falsefalseUSDtruefalse{us-gaap_StatementEquityComponentsAxis} : Accumulated Net Unrealized Investment Gain (Loss) [Member] 4/1/2010 - 3/31/2011 USD ($) $TwelveMonthsEnded_31Mar2011_Accumulated_Net_Unrealized_Investment_Gain_Loss_Memberhttp://www.sec.gov/CIK0000874663na0001-01-01T00:00:000001-01-01T00:00:00falsefalseus-gaap_AccumulatedNetUnrealizedInvestmentGainLossMemberus-gaap_StatementEquityComponentsAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_AccumulatedNetUnrealizedInvestmentGainLossMemberus-gaap_StatementEquityComponentsAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$8falsefalseUSDfalsefalse4/1/2010 - 3/31/2011 USD ($) USD ($) / shares $Apr-01-2010_Mar-31-2011http://www.sec.gov/CIK0000874663na0001-01-01T00:00:000001-01-01T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDEPSDividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0SharesStandardhttp://www.xbrl.org/2003/instancesharesxbrli0PureStandardhttp://www.xbrl.org/2003/instancepurexbrli0USDUSD$1false0us-gaap_SharesIssuedus-gaaptruenainstantNo definition available.falsefalsefalsetruefalsefalsefalsetruefalsefalseperiodstartlabelinstant2008-04-01T00:00:000001-01-01T00:00:001truefalsefalse102977348000102977348falsefalsefalsetruefalse2truefalsefalse382632000382632falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4truefalsefalse-7878182000-7878182falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseSharesxbrli:sharesItemTypesharesNumber of shares of stock issued as of the balance sheet date, including shares that had been issued and were previously outstanding but which are now held in the treasury.No authoritative reference available.falsefalseBeginning Balance, shares at Mar. 31, 20082false0us-gaap_StockholdersEquityus-gaaptruecreditinstantNo definition available.falsefalsefalsetruefalsefalsefalsetruefalsefalseperiodstartlabelinstant2008-04-01T00:00:000001-01-01T00:00:001truefalsefalse10300001030falsetruefalsetruefalse2truefalsefalse40004falsetruefalsetruefalse3truefalsefalse869695000869695falsetruefalsetruefalse4truefalsefalse-107322000-107322falsetruefalsetruefalse5truefalsefalse-456567000-456567falsetruefalsetruefalse6truefalsefalse-142000-142falsetruefalsetruefalse7truefalsefalse-1384000-1384falsetruefalsetruefalse8truefalsefalse305314000305314falsetruefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryTotal of all Stockholders' Equity (deficit) items, net of receivables from officers, directors owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A3 -Appendix A Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 4 -Section E Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30, 31 -Article 5 falsefalseBeginning Balance, value at Mar. 31, 20083false0us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1truefalsefalse10673150001067315falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseSharesxbrli:sharesItemTypesharesNumber of shares issued during the period as a result of any share-based compensation plan other than an employee stock ownership plan (ESOP).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 5 falsefalseIssuance of common stock under employee stock plans, shares4false0us-gaap_StockIssuedDuringPeriodValueShareBasedCompensationus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1truefalsefalse1000010falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3truefalsefalse70490007049falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse70590007059falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryValue of stock issued during the period as a result of any share-based compensation plan other than an employee stock ownership plan (ESOP).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30, 31 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 64 falsefalseIssuance of common stock under employee stock plans, value5false0alks_ReceiptOfCompanyStockForPurchaseOfStockOptionsOrToSatisfyMinimumTaxWithholdingObligationsRelatedToStockBasedAwardsSharesalksfalsenadurationReceipt of company stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock...falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4truefalsefalse-61607000-61607falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseSharesxbrli:sharesItemTypesharesReceipt of company stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock based awards shares.No authoritative reference available.falsefalseReceipt of Alkermes' stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock based awards, shares6false0alks_ReceiptOfCompanyStockForPurchaseOfStockOptionsOrToSatisfyMinimumTaxWithholdingObligationsRelatedToStockBasedAwardsValuealksfalsecreditdurationReceipt of company stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock...falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3truefalsefalse707000707falsefalsefalsetruefalse4truefalsefalse-707000-707falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryReceipt of company stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock based awards value.No authoritative reference available.falsefalseReceipt of Alkermes' stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock based awards, value7false0us-gaap_TreasuryStockSharesAcquiredus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4truefalsefalse-1569202000-1569202falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseSharesxbrli:sharesItemTypesharesNumber of shares that have been repurchased during the period and are being held in treasury.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 falsefalseRepurchase of common stock for treasury, at cost, shares8false0us-gaap_TreasuryStockValueAcquiredCostMethodus-gaaptruedebitdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsetruenegated1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4truefalsefalse-17996000-17996falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse-17996000-17996falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryCost of common and preferred stock that were repurchased during the period. Recorded using the cost method.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 1 -Section B -Paragraph 7 -Subparagraph b falsefalseRepurchase of common stock for treasury, at cost, value9false0us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValueus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3truefalsefalse1488400014884falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse1488400014884falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThis element represents the amount of recognized share-based compensation during the period, that is, the amount recognized as expense in the income statement (or as asset if compensation is capitalized).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 39 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 64 -Subparagraph b Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A91 falsefalseShare-based compensation10false0us-gaap_AdjustmentsToAdditionalPaidInCapitalTaxEffectFromShareBasedCompensationus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3truefalsefalse8000080falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse8000080falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryTax benefit associated with any share-based compensation plan other than an employee stock ownership plan (ESOP). The tax benefit results from the deduction by the entity on its tax return for an award of stock that exceeds the cumulative compensation cost for common stock or preferred stock recognized for financial reporting. Includes any resulting tax benefit that exceeds the previously recognized deferred tax asset (excess tax benefits).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 62 falsefalseExcess tax benefit from share-based compensation11false0us-gaap_OtherComprehensiveIncomeAvailableForSaleSecuritiesAdjustmentNetOfTaxPeriodIncreaseDecreaseus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7truefalsefalse-4958000-4958falsefalsefalsetruefalse8truefalsefalse-4958000-4958falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryGross appreciation or the gross loss in value of the total unsold securities at the end of an accounting period, after tax.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 14, 17, 19, 22, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 13 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph c(3) Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 24 -Subparagraph b falsefalseUnrealized gain/(loss) on marketable securities, net of tax $1,831 for 2010 and $225 for 201112false0us-gaap_NetIncomeLossus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5truefalsefalse130505000130505falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse130505000130505falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThe portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 19 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph d Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A7 -Appendix A Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph a Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 20 -Article 9 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 10, 15 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 87-21 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28, 29, 30 falsefalseNET INCOME (LOSS)13false0us-gaap_SharesIssuedus-gaaptruenainstantNo definition available.falsefalsefalsetruefalsefalsefalsefalsetruefalseperiodendlabelinstant2009-03-31T00:00:000001-01-01T00:00:001truefalsefalse104044663000104044663falsefalsefalsetruefalse2truefalsefalse382632000382632falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4truefalsefalse-9508451000-9508451falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseSharesxbrli:sharesItemTypesharesNumber of shares of stock issued as of the balance sheet date, including shares that had been issued and were previously outstanding but which are now held in the treasury.No authoritative reference available.falsefalseEnding Balance, shares at Mar. 31, 200914false0us-gaap_StockholdersEquityus-gaaptruecreditinstantNo definition available.falsefalsefalsetruefalsefalsefalsefalsetruefalseperiodendlabelinstant2009-03-31T00:00:000001-01-01T00:00:001truefalsefalse10400001040falsefalsefalsetruefalse2truefalsefalse40004falsefalsefalsetruefalse3truefalsefalse892415000892415falsefalsefalsetruefalse4truefalsefalse-126025000-126025falsefalsefalsetruefalse5truefalsefalse-326062000-326062falsefalsefalsetruefalse6truefalsefalse-142000-142falsefalsefalsetruefalse7truefalsefalse-6342000-6342falsefalsefalsetruefalse8truefalsefalse434888000434888falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryTotal of all Stockholders' Equity (deficit) items, net of receivables from officers, directors owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A3 -Appendix A Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 4 -Section E Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30, 31 -Article 5 falsefalseEnding Balance, value at Mar. 31, 200915false0us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1truefalsefalse770665000770665falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseSharesxbrli:sharesItemTypesharesNumber of shares issued during the period as a result of any share-based compensation plan other than an employee stock ownership plan (ESOP).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 5 falsefalseIssuance of common stock under employee stock plans, shares16false0us-gaap_StockIssuedDuringPeriodValueShareBasedCompensationus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1truefalsefalse70007falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3truefalsefalse25860002586falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse25930002593falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryValue of stock issued during the period as a result of any share-based compensation plan other than an employee stock ownership plan (ESOP).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30, 31 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 64 falsefalseIssuance of common stock under employee stock plans, value17false0alks_ReceiptOfCompanyStockForPurchaseOfStockOptionsOrToSatisfyMinimumTaxWithholdingObligationsRelatedToStockBasedAwardsSharesalksfalsenadurationReceipt of company stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock...falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4truefalsefalse-108410000-108410falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseSharesxbrli:sharesItemTypesharesReceipt of company stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock based awards shares.No authoritative reference available.falsefalseReceipt of Alkermes' stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock based awards, shares18false0alks_ReceiptOfCompanyStockForPurchaseOfStockOptionsOrToSatisfyMinimumTaxWithholdingObligationsRelatedToStockBasedAwardsValuealksfalsecreditdurationReceipt of company stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock...falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3truefalsefalse972000972falsefalsefalsetruefalse4truefalsefalse-972000-972falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryReceipt of company stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock based awards value.No authoritative reference available.falsefalseReceipt of Alkermes' stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock based awards, value19false0us-gaap_TreasuryStockSharesAcquiredus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4truefalsefalse-328404000-328404falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseSharesxbrli:sharesItemTypesharesNumber of shares that have been repurchased during the period and are being held in treasury.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 falsefalseRepurchase of common stock for treasury, at cost, shares20false0us-gaap_TreasuryStockValueAcquiredCostMethodus-gaaptruedebitdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsetruenegated1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4truefalsefalse-2684000-2684falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse-2684000-2684falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryCost of common and preferred stock that were repurchased during the period. Recorded using the cost method.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 43 -Chapter 1 -Section B -Paragraph 7 -Subparagraph b falsefalseRepurchase of common stock for treasury, at cost, value21false0us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValueus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3truefalsefalse1410700014107falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse1410700014107falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThis element represents the amount of recognized share-based compensation during the period, that is, the amount recognized as expense in the income statement (or as asset if compensation is capitalized).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 39 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 64 -Subparagraph b Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A91 falsefalseShare-based compensation22false0us-gaap_AdjustmentsToAdditionalPaidInCapitalTaxEffectFromShareBasedCompensationus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3truefalsefalse246000246falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse246000246falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryTax benefit associated with any share-based compensation plan other than an employee stock ownership plan (ESOP). The tax benefit results from the deduction by the entity on its tax return for an award of stock that exceeds the cumulative compensation cost for common stock or preferred stock recognized for financial reporting. Includes any resulting tax benefit that exceeds the previously recognized deferred tax asset (excess tax benefits).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 62 falsefalseExcess tax benefit from share-based compensation23false0us-gaap_OtherComprehensiveIncomeAvailableForSaleSecuritiesAdjustmentNetOfTaxPeriodIncreaseDecreaseus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7truefalsefalse30920003092falsefalsefalsetruefalse8truefalsefalse30920003092falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryGross appreciation or the gross loss in value of the total unsold securities at the end of an accounting period, after tax.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 14, 17, 19, 22, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 13 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph c(3) Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 24 -Subparagraph b falsefalseUnrealized gain/(loss) on marketable securities, net of tax $1,831 for 2010 and $225 for 201124false0us-gaap_NetIncomeLossus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5truefalsefalse-39626000-39626falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse-39626000-39626falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThe portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 19 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph d Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A7 -Appendix A Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph a Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 20 -Article 9 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 10, 15 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 87-21 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28, 29, 30 falsefalseNET INCOME (LOSS)25false0us-gaap_SharesIssuedus-gaaptruenainstantNo definition available.falsefalsefalsetruefalsefalsefalsefalsetruefalseperiodendlabelinstant2010-03-31T00:00:000001-01-01T00:00:001truefalsefalse104815328000104815328falsefalsefalsetruefalse2truefalsefalse382632000382632falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4truefalsefalse-9945265000-9945265falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseSharesxbrli:sharesItemTypesharesNumber of shares of stock issued as of the balance sheet date, including shares that had been issued and were previously outstanding but which are now held in the treasury.No authoritative reference available.falsefalseEnding Balance, shares at Mar. 31, 201026false0us-gaap_StockholdersEquityus-gaaptruecreditinstantNo definition available.falsefalsefalsetruefalsefalsefalsefalsetruefalseperiodendlabelinstant2010-03-31T00:00:000001-01-01T00:00:001truefalsefalse10470001047falsefalsefalsetruefalse2truefalsefalse40004falsefalsefalsetruefalse3truefalsefalse910326000910326falsefalsefalsetruefalse4truefalsefalse-129681000-129681falsefalsefalsetruefalse5truefalsefalse-365688000-365688falsefalsefalsetruefalse6truefalsefalse-142000-142falsefalsefalsetruefalse7truefalsefalse-3250000-3250falsefalsefalsetruefalse8truefalsefalse412616000412616falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryTotal of all Stockholders' Equity (deficit) items, net of receivables from officers, directors owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A3 -Appendix A Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 4 -Section E Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30, 31 -Article 5 falsefalseEnding Balance, value at Mar. 31, 201027false0us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1truefalsefalse956179000956179falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseSharesxbrli:sharesItemTypesharesNumber of shares issued during the period as a result of any share-based compensation plan other than an employee stock ownership plan (ESOP).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 5 falsefalseIssuance of common stock under employee stock plans, shares28false0us-gaap_StockIssuedDuringPeriodValueShareBasedCompensationus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1truefalsefalse80008falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3truefalsefalse47360004736falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse47440004744falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryValue of stock issued during the period as a result of any share-based compensation plan other than an employee stock ownership plan (ESOP).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30, 31 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 64 falsefalseIssuance of common stock under employee stock plans, value29false0alks_ReceiptOfCompanyStockForPurchaseOfStockOptionsOrToSatisfyMinimumTaxWithholdingObligationsRelatedToStockBasedAwardsSharesalksfalsenadurationReceipt of company stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock...falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4truefalsefalse-123943000-123943falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseSharesxbrli:sharesItemTypesharesReceipt of company stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock based awards shares.No authoritative reference available.falsefalseReceipt of Alkermes' stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock based awards, shares30false0alks_ReceiptOfCompanyStockForPurchaseOfStockOptionsOrToSatisfyMinimumTaxWithholdingObligationsRelatedToStockBasedAwardsValuealksfalsecreditdurationReceipt of company stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock...falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3truefalsefalse14140001414falsefalsefalsetruefalse4truefalsefalse-1414000-1414falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryReceipt of company stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock based awards value.No authoritative reference available.falsefalseReceipt of Alkermes' stock for the purchase of stock options or to satisfy minimum tax withholding obligations related to stock based awards, value31false0us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValueus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3truefalsefalse1981900019819falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse1981900019819falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThis element represents the amount of recognized share-based compensation during the period, that is, the amount recognized as expense in the income statement (or as asset if compensation is capitalized).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 39 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 64 -Subparagraph b Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A91 falsefalseShare-based compensation32false0us-gaap_AdjustmentsToAdditionalPaidInCapitalTaxEffectFromShareBasedCompensationus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3truefalsefalse00falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse00falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryTax benefit associated with any share-based compensation plan other than an employee stock ownership plan (ESOP). The tax benefit results from the deduction by the entity on its tax return for an award of stock that exceeds the cumulative compensation cost for common stock or preferred stock recognized for financial reporting. Includes any resulting tax benefit that exceeds the previously recognized deferred tax asset (excess tax benefits).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph 62 falsefalseExcess tax benefit from share-based compensation33false0us-gaap_OtherComprehensiveIncomeAvailableForSaleSecuritiesAdjustmentNetOfTaxPeriodIncreaseDecreaseus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7truefalsefalse379000379falsefalsefalsetruefalse8truefalsefalse379000379falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryGross appreciation or the gross loss in value of the total unsold securities at the end of an accounting period, after tax.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 14, 17, 19, 22, 26 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 13 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph c(3) Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 24 -Subparagraph b falsefalseUnrealized gain/(loss) on marketable securities, net of tax $1,831 for 2010 and $225 for 201134false0us-gaap_NetIncomeLossus-gaaptruecreditdurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1falsefalsefalse00falsefalsefalsetruefalse2falsefalsefalse00falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4falsefalsefalse00falsefalsefalsetruefalse5truefalsefalse-45540000-45540falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8truefalsefalse-45540000-45540falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryThe portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 19 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph d Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A7 -Appendix A Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph a Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 20 -Article 9 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 10, 15 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 87-21 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28, 29, 30 falsefalseNET INCOME (LOSS)35false0us-gaap_SharesIssuedus-gaaptruenainstantNo definition available.falsefalsefalsetruefalsefalsefalsefalsetruefalseperiodendlabelinstant2011-03-31T00:00:000001-01-01T00:00:001truefalsefalse105771507000105771507falsefalsefalsetruefalse2truefalsefalse382632000382632falsefalsefalsetruefalse3falsefalsefalse00falsefalsefalsetruefalse4truefalsefalse-10069208000-10069208falsefalsefalsetruefalse5falsefalsefalse00falsefalsefalsetruefalse6falsefalsefalse00falsefalsefalsetruefalse7falsefalsefalse00falsefalsefalsetruefalse8falsefalsefalse00falsefalsefalsefalsefalseSharesxbrli:sharesItemTypesharesNumber of shares of stock issued as of the balance sheet date, including shares that had been issued and were previously outstanding but which are now held in the treasury.No authoritative reference available.falsefalseEnding Balance, shares at Mar. 31, 201136false0us-gaap_StockholdersEquityus-gaaptruecreditinstantNo definition available.falsefalsefalsetruefalsefalsefalsefalsetruefalseperiodendlabelinstant2011-03-31T00:00:000001-01-01T00:00:001truefalsefalse10550001055falsetruefalsetruefalse2truefalsefalse40004falsetruefalsetruefalse3truefalsefalse936295000936295falsetruefalsetruefalse4truefalsefalse-131095000-131095falsetruefalsetruefalse5truefalsefalse-411228000-411228falsetruefalsetruefalse6truefalsefalse-142000-142falsetruefalsetruefalse7truefalsefalse-2871000-2871falsetruefalsetruefalse8truefalsefalse392018000392018falsetruefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryTotal of all Stockholders' Equity (deficit) items, net of receivables from officers, directors owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph A3 -Appendix A Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 4 -Section E Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30, 31 -Article 5 falsefalseEnding Balance, value at Mar. 31, 2011836Consolidated Statements of Shareholders' Equity (USD $)ThousandsThousandsUnKnownUnKnownfalsetrue