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Label Element Value
Risk Return [Abstract] rr_RiskReturnAbstract  
ProspectusDate rr_ProspectusDate Dec. 30, 2011
Bond Market Index Fund (Third Prospectus Summary) | Bond Market Index Fund
  
Risk Return [Abstract] rr_RiskReturnAbstract  
Risk/Return, Heading rr_RiskReturnHeading Bond Market Index Fund
Investment Objective, Heading rr_ObjectiveHeading Objective:
investment Objective, Primary rr_ObjectivePrimaryTextBlock 
The Fund seeks to provide current income.
Expense, Heading rr_ExpenseHeading Fees and Expenses of the Fund
Expense, Narrative rr_ExpenseNarrativeTextBlock 
This table describes the fees and expenses that you may pay if you buy and hold
shares of the Fund.
Shareholder Fees, Caption rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment): None
Operating Expenses, Caption rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover, Heading rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover 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 annualized portfolio turnover
rate was 84.6% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 84.60%
Expense Example, Heading rr_ExpenseExampleHeading Example
Expense Example, Narrative 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 that the
Fund's operating expenses remain the same. Although your actual costs may be
higher or lower, based on these assumptions your costs would be:
Investment Strategy, Heading rr_StrategyHeading Principal Investment Strategies
Investment Strategy, Narrative rr_StrategyNarrativeTextBlock 
Under normal circumstances, the Fund invests at least 80% of its net assets in
debt securities held by the Barclays Capital U.S. Aggregate Bond Index (the
"Index") at the time of purchase. The Index is composed of investment grade,
fixed rate debt issues, including government, corporate, asset-backed, and
mortgage-backed securities, with maturities of one year or more. The Fund
employs a passive investment approach designed to attempt to track the
performance of the Index. Under normal circumstances, the Fund maintains an
average portfolio duration that is in line with the duration of the Barclays
Capital U.S. Aggregate Bond Index, which as of August 31, 2011 was 5.05 years.
Risk, Heading rr_RiskHeading Principal Risks
Risk, Narrative rr_RiskNarrativeTextBlock 
The Fund may be an appropriate investment for investors interested in investing
in a fixed-income mutual fund and preferring a passive, rather than active,
management style.

The value of your investment in the Fund changes with the value of the Fund's
investments. Many factors affect that value, and it is possible to lose money by
investing in the Fund. An investment in the Fund is not a deposit of a bank and
is not insured or guaranteed by the Federal Deposit Insurance Corporation or any
other government agency. The principal risks of investing in the Fund, in
alphabetical order, are:

Fixed-Income Securities Risk. Fixed-income securities are subject to interest
rate risk and credit quality risk. The market value of fixed-income securities
generally declines when interest rates rise, and an issuer of fixed-income
securities could default on its payment obligations.

Index Fund Investment Risk. More likely than not, an index fund will not provide
investment performance that matches the index performance due to cashflows and
the fees and expenses of the fund.

Portfolio Duration Risk. Portfolio duration is a measure of the expected life of
a fixed-income security and its sensitivity to changes in interest rates. The
longer a fund's average portfolio duration, the more sensitive the fund will be
to changes in interest rates.

Prepayment Risk. Unscheduled prepayments on mortgage-backed and asset-backed
securities may have to be reinvested at lower rates. A reduction in prepayments
may increase the effective maturities of these securities, exposing them to the
risk of decline in market value over time (extension risk).

Real Estate Securities Risk. Real estate securities are subject to the risks
associated with direct ownership of real estate, including declines in value,
adverse economic conditions, increases in expenses, regulatory changes and
environmental problems.

Risk of Being an Underlying Fund. An underlying fund of a fund of funds may
experience relatively large redemptions or investments as the fund of funds
periodically reallocates or rebalances its assets. These transactions may cause
the underlying fund to sell portfolio securities to meet such redemptions, or to
invest cash from such investments, at times it would not otherwise do so, and
may as a result increase transaction costs and adversely affect underlying fund
performance.

U.S. Government Securities Risk. Yields available from U.S. government
securities are generally lower than yields from many other fixed-income
securities.

U.S. Government Sponsored Securities Risk. Securities issued by U.S.
government-sponsored or -chartered enterprises such as the Federal Home Loan
Mortgage Corporation, the Federal National Mortgage Association, and the Federal
Home Loan Banks are not issued or guaranteed by the U.S. Treasury.
Risk, Lose Money rr_RiskLoseMoney Many factors affect that value, and it is possible to lose money by investing in the Fund.
Risk, Not Insured Depository Institution rr_RiskNotInsuredDepositoryInstitution An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table, Heading rr_BarChartAndPerformanceTableHeading Performance
Performance, Narrative rr_PerformanceNarrativeTextBlock 
The following information provides an indication of the risks of investing in
the Fund. The bar chart shows the investment returns of the Fund's Class R-2
shares for each full calendar year of operations for 10 years (or, if shorter,
the life of the Fund). The table shows, for each share class of the Fund and for
the last one, five, and ten calendar year periods (or, if shorter, the life of
the Fund), how the Fund's average annual total returns compare to the returns of
one or more broad-based market indices. Past performance (before and after
taxes) is not necessarily an indication of how the Fund will perform in the
future. You may get updated performance information online at www.principal.com
or by calling 1-800-547-7754.

The R-1 through R-5 Class shares were first sold on December 30, 2009. For
periods prior to the date on which these classes began operations, their returns
are based on the performance of the Fund's Institutional Class shares adjusted
to reflect the fees and expenses of these classes. The adjustments result in
performance (for the periods prior to the date these classes began operations)
that is no higher than the historical performance of the Institutional Class
shares.
Performance, Information Illustrates Variability of Returns rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides an indication of the risks of investing in the Fund.
Performance, Availability Phone Number rr_PerformanceAvailabilityPhone 1-800-547-7754
Performance, Availability Website Address rr_PerformanceAvailabilityWebSiteAddress www.principal.com
Performance, Past Does Not Indicate Future rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart, Heading rr_BarChartHeading Total Returns as of December 31 each year (Class R-2 shares) [1]
Bar Chart, Closing rr_BarChartClosingTextBlock 
Highest return for a quarter during  Q2 '10 3.17%
the period of the bar chart above:

Lowest return for a quarter during   Q4 '10 -1.55%
the period of the bar chart above:
Index No Deduction for Fees, Expenses, Taxes rr_IndexNoDeductionForFeesExpensesTaxes reflects no deduction for fees, expenses, or taxes
Performance Table, Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table, Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred The after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns are shown for Class R-1 shares only and would be different for Class R-2, R-3, R-4 and R-5 shares.
Performance Table, Closing rr_PerformanceTableClosingTextBlock 
After-tax returns are calculated using the historical highest individual federal
marginal income tax rates and do not reflect the impact of state and local
taxes. Actual after-tax returns depend on an investor's tax situation and may
differ from those shown. The after-tax returns shown are not relevant to
investors who hold their Fund shares through tax-deferred arrangements, such as
401(k) plans or individual retirement accounts. After-tax returns are shown for
Class R-1 shares only and would be different for Class R-2, R-3, R-4 and R-5
shares.
Average Annual Returns, Caption rr_AverageAnnualReturnCaption Average Annual Total Returns For the periods ended December 31, 2010
Bond Market Index Fund (Third Prospectus Summary) | Bond Market Index Fund | Barclays Capital Aggregate Bond Index
  
Risk Return [Abstract] rr_RiskReturnAbstract  
Average Annual Returns, Label rr_AverageAnnualReturnLabel Barclays Capital Aggregate Bond Index (reflects no deduction for fees, expenses, or taxes)
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 6.54%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 6.35%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
Bond Market Index Fund (Third Prospectus Summary) | Bond Market Index Fund | Class R-1
  
Risk Return [Abstract] rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.35%
Other Expenses rr_OtherExpensesOverAssets 0.54%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.14%
Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets    [2]
Total Annual Fund Operating Expenses after Expense Reimbursement rr_NetExpensesOverAssets 1.14%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2012-12-31
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 116
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 362
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 628
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,386
Average Annual Returns, Label rr_AverageAnnualReturnLabel Class R-1 Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 4.96%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.84%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
Bond Market Index Fund (Third Prospectus Summary) | Bond Market Index Fund | Class R-1 | After Taxes on Distributions
  
Risk Return [Abstract] rr_RiskReturnAbstract  
Average Annual Returns, Label rr_AverageAnnualReturnLabel Class R-1 Return After Taxes on Distributions
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 4.45%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.34%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
Bond Market Index Fund (Third Prospectus Summary) | Bond Market Index Fund | Class R-1 | After Taxes on Distributions and Sales
  
Risk Return [Abstract] rr_RiskReturnAbstract  
Average Annual Returns, Label rr_AverageAnnualReturnLabel Class R-1 Return After Taxes on Distribution and Sale of Fund Shares
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 3.23%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 3.83%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
Bond Market Index Fund (Third Prospectus Summary) | Bond Market Index Fund | Class R-2
  
Risk Return [Abstract] rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.30%
Other Expenses rr_OtherExpensesOverAssets 0.46%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.01%
Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets    [2]
Total Annual Fund Operating Expenses after Expense Reimbursement rr_NetExpensesOverAssets 1.01%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2012-12-31
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 103
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 322
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 558
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,236
Annual Return 2010 rr_AnnualReturn2010 5.05%
Year to Date Return, Label rr_YearToDateReturnLabel The year-to-date return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Sep. 30, 2011
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 5.81%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest return for a quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2010
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 3.17%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest return for a quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2010
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (1.55%)
Average Annual Returns, Label rr_AverageAnnualReturnLabel Class R-2 Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.05%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.93%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
Bond Market Index Fund (Third Prospectus Summary) | Bond Market Index Fund | Class R-3
  
Risk Return [Abstract] rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.33%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.83%
Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets    [2]
Total Annual Fund Operating Expenses after Expense Reimbursement rr_NetExpensesOverAssets 0.83%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2012-12-31
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 85
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 265
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 460
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,025
Average Annual Returns, Label rr_AverageAnnualReturnLabel Class R-3 Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.31%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.19%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
Bond Market Index Fund (Third Prospectus Summary) | Bond Market Index Fund | Class R-4
  
Risk Return [Abstract] rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.10%
Other Expenses rr_OtherExpensesOverAssets 0.29%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.64%
Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets    [2]
Total Annual Fund Operating Expenses after Expense Reimbursement rr_NetExpensesOverAssets 0.64%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2012-12-31
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 65
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 205
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 357
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 798
Average Annual Returns, Label rr_AverageAnnualReturnLabel Class R-4 Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.47%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.35%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
Bond Market Index Fund (Third Prospectus Summary) | Bond Market Index Fund | Class R-5
  
Risk Return [Abstract] rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets   
Other Expenses rr_OtherExpensesOverAssets 0.27%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.52%
Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets    [2]
Total Annual Fund Operating Expenses after Expense Reimbursement rr_NetExpensesOverAssets 0.52%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2012-12-31
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 53
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 167
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 291
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 653
Average Annual Returns, Label rr_AverageAnnualReturnLabel Class R-5 Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.64%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.51%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
[1] The year-to-date return as of September 30, 2011 was 5.81% for Class R-2 shares.
[2] Principal Management Corporation ("Principal") has contractually agreed to limit the Fund's expenses attributable to Class R-1, R-2, R-3, R-4, and R-5 shares and, if necessary, pay expenses normally payable by the Fund, excluding interest expense, through the period ending December 31, 2012. The expense limit will maintain a total level of operating expenses (expressed as a percent of average net assets on an annualized basis) not to exceed 1.18% for Class R-1, 1.05% for Class R-2, 0.87% for Class R-3, 0.68% for Class R-4, and 0.56% for Class R-5. It is expected that the expense limit will continue through the period disclosed; however, Principal Funds, Inc. and Principal, the parties to the agreement, may agree to terminate the expense limit prior to the end of the period.