Risk Return Summary [Abstract] Risk Return Summary [Abstract] Prospectus: Prospectus: Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] S000003923 [Member] DELAWARE EXTENDED DURATION BOND FUND S000003923 [Member] Risk/Return: Risk/Return: Risk/Return [Heading] Risk/Return [Heading] Objective [Heading] Objective [Heading] Objective, Primary [Text Block] Objective, Primary [Text Block] Expense [Heading] Expense [Heading] Expense Narrative [Text Block] Expense Narrative [Text Block] Shareholder Fees Caption [Text] Shareholder Fees Caption [Text] Shareholder Fees [Table] Shareholder Fees [Table] Operating Expenses Caption [Text] Operating Expenses Caption [Text] Annual Fund Operating Expenses [Table] Annual Fund Operating Expenses [Table] Expense Example [Heading] Expense Example [Heading] Expense Example Narrative [Text Block] Expense Example Narrative [Text Block] Expense Example, With Redemption [Table] Expense Example, With Redemption [Table] Expense Example, No Redemption, By Year, Caption [Text] Expense Example, No Redemption, By Year, Caption [Text] Expense Example, No Redemption [Table] Expense Example, No Redemption [Table] Portfolio Turnover [Heading] Portfolio Turnover [Heading] Portfolio Turnover [Text Block] Portfolio Turnover [Text Block] Strategy [Heading] Strategy [Heading] Strategy Narrative [Text Block] Strategy Narrative [Text Block] Risk [Heading] Risk [Heading] Risk Narrative [Text Block] Risk Narrative [Text Block] Bar Chart and Performance Table [Heading] Bar Chart and Performance Table [Heading] Performance Narrative [Text Block] Performance Narrative [Text Block] Bar Chart [Heading] Bar Chart [Heading] Bar Chart [Table] Bar Chart [Table] Bar Chart Closing [Text Block] Bar Chart Closing [Text Block] Performance Table Heading Performance Table Heading Performance [Table] Performance [Table] Performance Table Footnotes Performance Table Footnotes Performance Table Closing [Text Block] Performance Table Closing [Text Block] Share Class [Axis] Share Class [Axis] Share Classes Share Classes C000011010 [Member] CLASS A C000011010 [Member] C000011011 [Member] CLASS B C000011011 [Member] C000011012 [Member] CLASS C C000011012 [Member] C000011013 [Member] CLASS R C000011013 [Member] C000011014 [Member] INSTITUTIONAL CLASS C000011014 [Member] Shareholder Fees: Shareholder fees (fees paid directly from your investment) Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) Maximum sales charge (load) imposed on purchases as a percentage of offering price Maximum Deferred Sales Charge (as a percentage of Offering Price) Maximum contingent deferred sales charge (load) as a percentage of original purchase price or redemption price, whichever is lower Maximum contingent deferred sales charge (load) as a percentage of original percentage price or redemption price, whichever is lower Operating Expenses: Operating Expenses: Management Fees (as a percentage of Assets) Management fees Distribution and Service (12b-1) Fees Distribution and service (12b-1) fees Other Expenses (as a percentage of Assets): Other expenses Expenses (as a percentage of Assets) Total annual fund operating expenses Fee Waiver or Reimbursement Fee waivers and expense reimbursements Net Expenses (as a percentage of Assets) Total annual fund operating expenses after fee waivers and expense reimbursements Expense Example: Expense Example: Expense Example, with Redemption, 1 Year 1 year Expense Example, with Redemption, 3 Years 3 years Expense Example, with Redemption, 5 Years 5 years Expense Example, with Redemption, 10 Years 10 years Expense Example, No Redemption: Expense Example, No Redemption: Expense Example, No Redemption, 1 Year 1 year Expense Example, No Redemption, 3 Years 3 years Expense Example, No Redemption, 5 Years 5 years Expense Example, No Redemption, 10 Years 10 years Bar Chart Table: Bar Chart Table: Annual Return 2002 Annual Return 2002 Annual Return 2003 Annual Return 2003 Annual Return 2004 Annual Return 2004 Annual Return 2005 Annual Return 2005 Annual Return 2006 Annual Return 2006 Annual Return 2007 Annual Return 2007 Annual Return 2008 Annual Return 2008 Annual Return 2009 Annual Return 2009 Annual Return 2010 Annual Return 2010 Annual Return 2011 Annual Return 2011 Performance Measure [Axis] Performance Measure [Axis] Before Taxes Before Taxes After Taxes on Distributions After Taxes on Distributions After Taxes on Distributions After Taxes on Distributions and Sales After Taxes on Distributions and sale of Fund shares After Taxes on Distributions and sale of Fund shares Barclays Long U.S. Corporate Index [Member] Barclays Long U.S. Corporate Index (reflects no deduction for fees, expenses, or taxes) Barclays Long U.S. Corporate Index [Member] Average Annual Return: Average Annual Return: Label Label 1 Year 1 year 5 Years 5 years 10 Years 10 years or lifetime Since Inception lifetime Inception Date Inception Date Document Type Document Type Document Period End Date Document Period End Date Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Amendment Flag Amendment Flag Document Creation Date Document Creation Date Document Effective Date Document Effective Date Prospectus Date Prospectus Date Fee Waiver or Reimbursement over Assets, Date of Termination Fee Waiver or Reimbursement over Assets, Date of Termination Portfolio Turnover, Rate Portfolio Turnover, Rate Expense Breakpoint Discounts [Text] Expense Breakpoint Discounts [Text] Expense Breakpoint, Minimum Investment Required [Amount] Expense Breakpoint, Minimum Investment Required [Amount] Strategy Portfolio Concentration [Text] Strategy Portfolio Concentration [Text] Risk Lose Money [Text] Risk Lose Money [Text] Risk Not Insured Depository Institution [Text] Risk Not Insured Depository Institution [Text] Performance Information Illustrates Variability of Returns [Text] Performance Information Illustrates Variability of Returns [Text] Performance Availability Phone [Text] Performance Availability Phone [Text] Performance Availability Website Address [Text] Performance Availability Website Address [Text] Performance Past Does Not Indicate Future [Text] Performance Past Does Not Indicate Future [Text] Bar Chart Does Not Reflect Sales Loads [Text] Bar Chart Does Not Reflect Sales Loads [Text] Year to Date Return, Label Year to Date Return, Label Bar Chart, Year to Date Return, Date Bar Chart, Year to Date Return, Date Bar Chart, Year to Date Return Bar Chart, Year to Date Return Highest Quarterly Return, Label Highest Quarterly Return, Label Highest Quarterly Return, Date Highest Quarterly Return, Date Highest Quarterly Return Highest Quarterly Return Lowest Quarterly Return, Label Lowest Quarterly Return, Label Lowest Quarterly Return, Date Lowest Quarterly Return, Date Lowest Quarterly Return Lowest Quarterly Return Index No Deduction for Fees, Expenses, Taxes [Text] Index No Deduction for Fees, Expenses, Taxes [Text] Performance Table Uses Highest Federal Rate Performance Table Uses Highest Federal Rate Performance Table Not Relevant to Tax Deferred Performance Table Not Relevant to Tax Deferred Performance Table One Class of after Tax Shown [Text] Performance Table One Class of after Tax Shown [Text] Document Information, Document [Axis] Document [Domain] Expense Example, No Redemption Narrative [Text Block] Risk Closing [Text Block] Bar Chart Narrative [Text Block] Bar Chart Footnotes [Text Block] Performance Table Narrative Maximum Cumulative Sales Charge (as a percentage of Offering Price) Operating Expenses Column [Text] Expenses Restated to Reflect Current [Text] Risk Nondiversified Status [Text] Performance Table Does Reflect Sales Loads Performance Table Explanation after Tax Higher