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Label Element Value
(Delaware Extended Duration Bond Fund)  
Prospectus: rr_ProspectusTable  
Objective [Heading] rr_ObjectiveHeading

What is the Fund's investment objective?

Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

Delaware Extended Duration Bond Fund seeks to provide investors with total return.

Expense [Heading] rr_ExpenseHeading

What are the Fund's fees and expenses?

Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

The table below describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales-charge discounts if you and your family invest, or agree to invest in the future, at least $100,000 in Delaware Investments® Funds. More information about these and other discounts is available from your financial intermediary, in the Fund's prospectus under the section entitled "About your account," and in the Fund's statement of additional information (SAI) under the section entitled "Purchasing Shares."

Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales-charge discounts if you and your family invest, or agree to invest in the future, at least $100,000 in Delaware Investments® Funds. More information about these and other discounts is available from your financial intermediary, in the Fund's prospectus under the section entitled "About your account," and in the Fund's statement of additional information (SAI) under the section entitled "Purchasing Shares."
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 100,000
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption

Shareholder fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption

Annual fund operating expenses (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination April 30, 2017
Expense Example [Heading] rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and reflects the Manager's expense waivers and reimbursements for the 1-year contractual period and the total operating expenses without waivers for years 2 through 10. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading

Portfolio turnover

Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 185% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 185.00%
Strategy [Heading] rr_StrategyHeading

What are the Fund's principal investment strategies?

Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund will invest at least 80% of its net assets, plus the amount of any borrowings for investment purposes, in corporate bonds (80% policy). Delaware Management Company (Manager) focuses on corporate bonds that have investment grade credit ratings from a nationally recognized statistical rating organization (NRSRO). The bonds the Manager selects for the portfolio are typically rated BBB- and above by Standard & Poor's Financial Services LLC (S&P), Baa3 and above by Moody's Investors Service, Inc. (Moody's), or similarly rated by another NRSRO. The Manager may also invest in unrated bonds if it believes their credit quality is comparable to those that have investment grade ratings.

The Fund may also invest up to 20% of its net assets in high yield corporate bonds ("junk bonds"). In addition, the Fund may invest up to 40% of its total assets in foreign securities, but the Fund's total non-U.S.-dollar currency exposure will be limited, in the aggregate, to no more than 25% of net assets.

The average portfolio duration of the Fund will generally vary within two years (plus or minus) of the current average duration of the Barclays Long U.S. Corporate Index, which as of Oct. 31, 2015, was 13.53 years. Duration measures a bond's sensitivity to interest rates by indicating the approximate change in a bond or bond fund's price given a 1% change in interest rates. In general, securities with longer durations are more sensitive to interest rate changes.

The 80% policy is nonfundamental and may be changed without shareholder approval. Fund shareholders would be given at least 60 days' notice prior to any such change.
Risk [Heading] rr_RiskHeading

What are the principal risks of investing in the Fund?

Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

Investing in any mutual fund involves the risk that you may lose part or all of the money you invest. Over time, the value of your investment in the Fund will increase and decrease according to changes in the value of the securities in the Fund's portfolio. Principal risks include:

Market risk — The risk that all or a majority of the securities in a certain market — such as the stock or bond market — will decline in value because of factors such as adverse political or economic conditions, future expectations, investor confidence, or heavy institutional selling.

Interest rate risk — The risk that securities will decrease in value if interest rates rise. This risk is generally associated with bonds.

Credit risk — The risk that an issuer of a debt security, including a governmental issuer or an entity that insures a bond, may be unable to make interest payments and repay principal in a timely manner.

High yield (junk bond) risk — The risk that high yield securities, commonly known as "junk bonds," are subject to reduced creditworthiness of issuers; increased risk of default and a more limited and less liquid secondary market; and greater price volatility and risk of loss of income and principal than are higher-rated securities. High yield bonds are sometimes issued by municipalities that have less financial strength and therefore have less ability to make projected debt payments on the bonds.

Loans and other indebtedness risk — The risk that the portfolio will not receive payment of principal, interest, and other amounts due in connection with these investments and will depend primarily on the financial condition of the borrower and the lending institution. A portfolio's ability to sell its loans or to realize their full value upon sale may also be impaired due to the lack of an active trading market, irregular trading activity, wide bid/ask spreads, contractual restrictions, and extended trade settlement periods. In addition, certain loans in which a fund invests may not be considered securities. A fund therefore may not be able to rely upon the anti-fraud provisions of the federal securities laws with respect to these investments.

Foreign risk — The risk that foreign securities (particularly in emerging markets) may be adversely affected by political instability, changes in currency exchange rates, inefficient markets and higher transaction costs, foreign economic conditions, the imposition of economic or trade sanctions, or inadequate or different regulatory and accounting standards.

Liquidity risk — The possibility that securities cannot be readily sold within seven days at approximately the price at which a portfolio has valued them.

Government and regulatory risk — The risk that governments or regulatory authorities have, from time to time, taken or considered actions that could adversely affect various sectors of the securities markets and significantly affect fund performance.

Investments not guaranteed by Delaware Management Company (Manager) or its affiliates — Neither the Manager nor its affiliates noted in this document are authorized deposit-taking institutions for the purposes of the Banking Act 1959 (Commonwealth of Australia). The obligations of these entities do not represent deposits or other liabilities of Macquarie Bank Limited (MBL). MBL does not guarantee or otherwise provide assurance in respect of the obligations of these entities, unless noted otherwise.
Risk Lose Money [Text] rr_RiskLoseMoney Investing in any mutual fund involves the risk that you may lose part or all of the money you invest. Over time, the value of your investment in the Fund will increase and decrease according to changes in the value of the securities in the Fund's portfolio.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading

How has Delaware Extended Duration Bond Fund performed?

Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual total returns for the 1-, 5-, and 10-year periods compare with those of a broad measure of market performance. The Fund's past performance (before and after taxes) is not necessarily an indication of how it will perform in the future. The returns reflect any expense caps in effect during these periods. The returns would be lower without the expense caps. You may obtain the Fund's most recently available month-end performance by calling 800 523-1918 or by visiting our website at delawareinvestments.com/performance.
Bar Chart [Heading] rr_BarChartHeading

Year-by-year total return (Class A)

Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

As of March. 31, 2016, the Fund's Class A shares had a calendar year-to-date return of 5.38%. During the periods illustrated in this bar chart, Class A's highest quarterly return was 14.88% for the quarter ended June 30, 2009 and its lowest quarterly return was -8.61% for the quarter ended Sept. 30, 2008. The maximum Class A sales charge of 4.50%, which is normally deducted when you purchase shares, is not reflected in the highest/lowest quarterly returns or in the bar chart. If this fee were included, the returns would be less than those shown. The average annual returns in the table below do include the sales charge.

Class R6 shares have not commenced operations as of the date of this Prospectus and are therefore not included below.

Performance Table Heading rr_PerformanceTableHeading

Average annual total returns for periods ended December 31, 2015

Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax performance is presented only for Class A shares of the Fund. The after-tax returns for other Fund classes may vary. Actual after-tax returns depend on the investor's individual tax situation and may differ from the returns shown. After-tax returns are not relevant for shares held in tax-deferred investment vehicles such as employer-sponsored 401(k) plans and individual retirement accounts (IRAs). The after-tax returns shown are calculated using the highest individual federal marginal income tax rates in effect during the periods presented and do not reflect the impact of state and local taxes.
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate The after-tax returns shown are calculated using the highest individual federal marginal income tax rates in effect during the periods presented and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred After-tax returns are not relevant for shares held in tax-deferred investment vehicles such as employer-sponsored 401(k) plans and individual retirement accounts (IRAs).
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund's past performance (before and after taxes) is not necessarily an indication of how it will perform in the future.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax performance is presented only for Class A shares of the Fund.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress delawareinvestments.com/performance
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800 523-1918
(Delaware Extended Duration Bond Fund) | Barclays Long U.S. Corporate Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 15.73%
5 Years rr_AverageAnnualReturnYear05 9.60%
10 years or lifetime rr_AverageAnnualReturnYear10 6.99%
(Delaware Extended Duration Bond Fund) | Class A  
Prospectus: rr_ProspectusTable  
Maximum sales charge (load) imposed on purchases as a percentage of offering price rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.50%
Maximum contingent deferred sales charge (load) as a percentage of original purchase price or redemption price, whichever is lower rr_MaximumDeferredSalesChargeOverOfferingPrice none
Management fees rr_ManagementFeesOverAssets 0.54%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 1.00%
Fee waivers and expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.04%) [1]
Total annual fund operating expenses after fee waivers and expense reimbursements rr_NetExpensesOverAssets 0.96%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 544
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 750
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 974
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,616
Annual Return 2006 rr_AnnualReturn2006 5.33%
Annual Return 2007 rr_AnnualReturn2007 3.02%
Annual Return 2008 rr_AnnualReturn2008 (2.85%)
Annual Return 2009 rr_AnnualReturn2009 24.96%
Annual Return 2010 rr_AnnualReturn2010 14.31%
Annual Return 2011 rr_AnnualReturn2011 16.50%
Annual Return 2012 rr_AnnualReturn2012 16.40%
Annual Return 2013 rr_AnnualReturn2013 (4.00%)
Annual Return 2014 rr_AnnualReturn2014 15.90%
Annual Return 2015 rr_AnnualReturn2015 (4.77%)
Year to Date Return, Label rr_YearToDateReturnLabel As of March. 31, 2016, the Fund's Class A shares had a calendar year-to-date return of 5.38%.
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 5.38%
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2016
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest quarterly return was 14.88% for the quarter ended June 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 14.88%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest quarterly return was -8.61% for the quarter ended Sept. 30, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (8.61%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
1 Year rr_AverageAnnualReturnYear01 (9.04%)
5 Years rr_AverageAnnualReturnYear05 6.52%
10 years or lifetime rr_AverageAnnualReturnYear10 7.52%
(Delaware Extended Duration Bond Fund) | Class A | return after taxes on distributions  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 (10.61%)
5 Years rr_AverageAnnualReturnYear05 3.81%
10 years or lifetime rr_AverageAnnualReturnYear10 4.92%
(Delaware Extended Duration Bond Fund) | Class A | return after taxes on distributions and sale of Fund shares  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 (5.06%)
5 Years rr_AverageAnnualReturnYear05 4.12%
10 years or lifetime rr_AverageAnnualReturnYear10 4.93%
(Delaware Extended Duration Bond Fund) | Class C  
Prospectus: rr_ProspectusTable  
Maximum sales charge (load) imposed on purchases as a percentage of offering price rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum contingent deferred sales charge (load) as a percentage of original purchase price or redemption price, whichever is lower rr_MaximumDeferredSalesChargeOverOfferingPrice 1.00% [2]
Management fees rr_ManagementFeesOverAssets 0.54%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 1.75%
Fee waivers and expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.04%) [1]
Total annual fund operating expenses after fee waivers and expense reimbursements rr_NetExpensesOverAssets 1.71%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 274
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 547
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 945
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,059
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 174
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 547
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 945
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,059
1 Year rr_AverageAnnualReturnYear01 (6.40%)
5 Years rr_AverageAnnualReturnYear05 6.72%
10 years or lifetime rr_AverageAnnualReturnYear10 7.24%
(Delaware Extended Duration Bond Fund) | Class R  
Prospectus: rr_ProspectusTable  
Maximum sales charge (load) imposed on purchases as a percentage of offering price rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum contingent deferred sales charge (load) as a percentage of original purchase price or redemption price, whichever is lower rr_MaximumDeferredSalesChargeOverOfferingPrice none
Management fees rr_ManagementFeesOverAssets 0.54%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 1.25%
Fee waivers and expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.04%) [1]
Total annual fund operating expenses after fee waivers and expense reimbursements rr_NetExpensesOverAssets 1.21%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 123
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 393
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 682
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,508
1 Year rr_AverageAnnualReturnYear01 (5.00%)
5 Years rr_AverageAnnualReturnYear05 7.24%
10 years or lifetime rr_AverageAnnualReturnYear10 7.76%
(Delaware Extended Duration Bond Fund) | Institutional Class  
Prospectus: rr_ProspectusTable  
Maximum sales charge (load) imposed on purchases as a percentage of offering price rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum contingent deferred sales charge (load) as a percentage of original purchase price or redemption price, whichever is lower rr_MaximumDeferredSalesChargeOverOfferingPrice none
Management fees rr_ManagementFeesOverAssets 0.54%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.75%
Fee waivers and expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.04%) [1]
Total annual fund operating expenses after fee waivers and expense reimbursements rr_NetExpensesOverAssets 0.71%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 73
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 236
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 413
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 927
1 Year rr_AverageAnnualReturnYear01 (4.55%)
5 Years rr_AverageAnnualReturnYear05 7.79%
10 years or lifetime rr_AverageAnnualReturnYear10 8.30%
(Delaware Extended Duration Bond Fund) | Class R6  
Prospectus: rr_ProspectusTable  
Maximum sales charge (load) imposed on purchases as a percentage of offering price rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum contingent deferred sales charge (load) as a percentage of original purchase price or redemption price, whichever is lower rr_MaximumDeferredSalesChargeOverOfferingPrice none
Management fees rr_ManagementFeesOverAssets 0.54%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.13% [3]
Total annual fund operating expenses rr_ExpensesOverAssets 0.67%
Fee waivers and expense reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.04%) [1]
Total annual fund operating expenses after fee waivers and expense reimbursements rr_NetExpensesOverAssets 0.63%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 64
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 210
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 369
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 831
[1] The Fund's investment manager, Delaware Management Company (Manager), has contractually agreed to waive all or a portion of its investment advisory fees and/or pay/reimburse expenses (excluding any 12b-1 fees, acquired fund fees and expenses, taxes, interest, short sale and dividend interest expenses, brokerage fees, certain insurance costs, and nonroutine expenses or costs, including, but not limited to, those relating to reorganizations, litigation, conducting shareholder meetings, and liquidations) in order to prevent total annual fund operating expenses from exceeding 0.71% of the Fund's average daily net assets from April 30, 2016 through April 30, 2017 for all share classes other than Class R6, and 0.63% of the Fund's Class R6 shares' average daily net assets from April 30, 2016 through April 30, 2017. These waivers and reimbursements may only be terminated by agreement of the Manager and the Fund.
[2] Class C shares redeemed within one year of purchase are subject to a 1.00% contingent deferred sales charge (CDSC).
[3] "Other expenses" for Class R6 are estimated and account for Class R6 shares not being subject to certain expenses as described further in the section of the prospectus entitled "Choosing a share class."