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Label Element Value
Risk Return [Abstract] rr_RiskReturnAbstract  
ProspectusDate rr_ProspectusDate Dec. 30, 2011
International Equity Index Fund (Second Prospectus Summary) | International Equity Index Fund
  
Risk Return [Abstract] rr_RiskReturnAbstract  
Risk/Return, Heading rr_RiskReturnHeading International Equity Index Fund
Investment Objective, Heading rr_ObjectiveHeading Objective:
investment Objective, Primary rr_ObjectivePrimaryTextBlock 
The Fund seeks long-term growth of capital.
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 31.4% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 31.40%
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
securities held by MSCI EAFE Index (the "Index") at the time of purchase. The
Index is a weighted equity index designed to measure the equity performance of
developed markets (Europe, Australasia, Far East), excluding the United States
and Canada. The Fund employs a passive investment approach designed to attempt
to track the performance of the Index. The Fund invests in index futures and
options and exchange-traded funds ("ETFs") on a daily basis to gain exposure to
the Index in an effort to minimize tracking error relative to the benchmark.
Risk, Heading rr_RiskHeading Principal Risks
Risk, Narrative rr_RiskNarrativeTextBlock 
The Fund may be an appropriate investment for investors seeking long-term growth
of capital, willing to accept the potential for volatile fluctuations in the
value of investments 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:

Derivatives Risk. Transactions in derivatives (such as options, futures,
currency contracts, and swaps) may increase volatility, cause the liquidation of
portfolio positions when not advantageous to do so and produce disproportionate
losses.

Equity Securities Risk. Equity securities (common, convertible preferred stocks
and other securities whose values are tied to the price of stocks, such as
rights, warrants and convertible debt securities) could decline in value if the
issuer's financial condition declines or in response to overall market and
economic conditions. A fund's principal market segment(s), such as large cap,
mid cap or small cap stocks, or growth or value stocks, may underperform other
market segments or the equity markets as a whole. Investments in smaller
companies and mid-size companies may involve greater risk and price volatility
than investments in larger, more mature companies.

Exchange-Traded Funds ("ETFs") Risk. An ETF is subject to the risks associated
with direct ownership of the securities comprising the index on which the ETF is
based. Fund shareholders indirectly bear their proportionate share of the
expenses of the ETFs in which the fund invests.

Foreign Securities Risk. The risks of foreign securities include loss of value
as a result of: political or economic instability; nationalization,
expropriation or confiscatory taxation; changes in foreign exchange rates and
foreign exchange restrictions; settlement delays; and limited government
regulation (including less stringent reporting, accounting, and disclosure
standards than are required of U.S. companies).

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.

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.
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.

Life of Fund returns are measured from the date the Classes R-1, R-2, R-3, R-4,
and R-5 shares were first sold December 30, 2009.
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    Q3 '10 17.10%
the period of the bar chart above:

Lowest return for a quarter during     Q2 '10 -15.28%
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 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.
Performance Table, One Class of after Tax Shown rr_PerformanceTableOneClassOfAfterTaxShown 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
International Equity Index Fund (Second Prospectus Summary) | International Equity Index Fund | MSCI - EAFE NDTR D Index
  
Risk Return [Abstract] rr_RiskReturnAbstract  
Average Annual Returns, Label rr_AverageAnnualReturnLabel MSCI - EAFE NDTR D Index (reflects no deduction for fees, expenses, or taxes)
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 7.75%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 8.25%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
International Equity Index Fund (Second Prospectus Summary) | International Equity 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 0.66%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.27%
Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets    [2]
Total Annual Fund Operating Expenses after Expense Reimbursement rr_NetExpensesOverAssets 1.27%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2012-12-31
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 129
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 403
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 697
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,534
Average Annual Returns, Label rr_AverageAnnualReturnLabel Class R-1 Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.34%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.32%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
International Equity Index Fund (Second Prospectus Summary) | International Equity 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 5.06%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.04%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
International Equity Index Fund (Second Prospectus Summary) | International Equity 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 3.83%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.52%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
International Equity Index Fund (Second Prospectus Summary) | International Equity 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 0.58%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
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
Annual Return 2010 rr_AnnualReturn2010 5.46%
Year to Date Return, Label rr_YearToDateReturnLabel 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 Sep. 30, 2010
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 17.10%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest return for a quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2010
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (15.28%)
Average Annual Returns, Label rr_AverageAnnualReturnLabel Class R-2 Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.46%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.44%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
International Equity Index Fund (Second Prospectus Summary) | International Equity 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 0.45%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.96%
Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets    [2]
Total Annual Fund Operating Expenses after Expense Reimbursement rr_NetExpensesOverAssets 0.96%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2012-12-31
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 98
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 306
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 531
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,178
Average Annual Returns, Label rr_AverageAnnualReturnLabel Class R-3 Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.58%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.57%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
International Equity Index Fund (Second Prospectus Summary) | International Equity 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 0.41%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.77%
Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets    [2]
Total Annual Fund Operating Expenses after Expense Reimbursement rr_NetExpensesOverAssets 0.77%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2012-12-31
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 79
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 246
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 428
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 954
Average Annual Returns, Label rr_AverageAnnualReturnLabel Class R-4 Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.91%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.89%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2009
International Equity Index Fund (Second Prospectus Summary) | International Equity 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 0.39%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.65%
Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets    [2]
Total Annual Fund Operating Expenses after Expense Reimbursement rr_NetExpensesOverAssets 0.65%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2012-12-31
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 66
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 208
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 362
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 810
Average Annual Returns, Label rr_AverageAnnualReturnLabel Class R-5 Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.98%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.96%
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 and Acquired Fund Fees and Expenses, 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 1.28% for Class R-1, 1.15% for Class R-2, 0.97% for Class R-3, 0.78% for Class R-4, and 0.66% 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.