Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Jun. 13, 2012
Opportunistic Municipal Fund (Prospectus Summary) | Opportunistic Municipal Fund
Risk Return [Abstract]	rr_RiskReturnAbstract
Risk/Return, Heading	rr_RiskReturnHeading	Opportunistic Municipal Fund
Investment Objective, Heading	rr_ObjectiveHeading	Objective:
investment Objective, Primary	rr_ObjectivePrimaryTextBlock	The Fund seeks to provide a high level of income that is exempt from federal income tax while protecting investors' 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. 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 Principal Funds, Inc. More information about these and other discounts is available from your financial professional and in "Choosing a Share Class and The Costs of Investing" beginning on page 38 of the Fund's prospectus and "Multiple Class Structure" beginning on page 59 of the Fund's Statement of Additional Information.
Shareholder Fees, Caption	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
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. This is a new Fund and does not yet have a portfolio turnover rate to disclose.
Expense Breakpoint, Discounts	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 Principal Funds, Inc.
Expense Breakpoint, Minimum Investment Required Amount	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	100,000
Other Expenses, New Fund, Based on Estimates	rr_OtherExpensesNewFundBasedOnEstimates	Other Expenses are estimated for the year ending August 31, 2012.
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:
Expense Example, No Redemption, By Year, Caption	rr_ExpenseExampleNoRedemptionByYearCaption	You would pay the following expenses if you did not redeem your shares:
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, plus borrowings for investment purposes, in municipal obligations (securities issued by or on behalf of state or local governments and other public authorities). Municipal obligations pay interest that is exempt from federal income tax. The Fund has a flexible investment strategy and may invest in obligations of any duration and credit quality, including below investment grade bonds (rated at the time of purchase Ba1 or lower by Moody's or BB+ or lower by S&P, sometimes called "junk bonds") as rated by at least one independent rating agency, or if unrated, judged to be of comparable quality by the Fund's Sub-Advisor. The Fund may invest in other debt obligations, including (but not limited to) taxable municipal obligations, U.S. Treasury securities, obligations of the U.S. Government, its agencies and instrumentalities ("Agency Securities") and inverse floating rate obligations, which are generally more volatile than other types of municipal obligations. The Fund may invest in exchange-traded funds (ETFs) to gain exposure to the municipal market. The Fund may purchase derivative instruments, which derive their value from another instrument, security or index. The Fund may purchase or sell various kinds of financial futures contracts to hedge against changes in interest rates or as a substitute for the purchase of portfolio securities. The Fund also may enter into interest rate swaps and credit derivatives, which may include credit default swaps.
Risk, Heading	rr_RiskHeading	Principal Risks
Risk, Narrative	rr_RiskNarrativeTextBlock	The Fund may be an appropriate investment for investors who are seeking monthly, federally tax-exempt dividends to produce income or to reinvest for modest growth and are willing to accept fluctuations in the value of their investment. 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:    Counterparty Risk. Counterparty risk is the risk that the counterparty to a derivatives contract or repurchase agreement, the borrower of a portfolio's securities, or other obligation, will be unable or unwilling to make timely principal, interest, or settlement payments, or otherwise to honor its obligations.    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. 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.    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.    High Yield Securities Risk. High yield fixed-income securities (commonly referred to as "junk bonds") are subject to greater credit quality risk than higher rated fixed-income securities and should be considered speculative.    Inverse Floating Rate Investments. Inverse floating rate investments are extremely sensitive to changes in interest rates and in some cases their market value may be extremely volatile. Leverage Risk. Leverage created by borrowing or certain types of transactions or investments, such as reverse repurchase agreements, loans of portfolio securities, and the use of when-issued, delayed delivery or forward commitment transactions, or derivative instruments, may impair the fund's liquidity, cause it to liquidate positions at an unfavorable time, increase volatility of the fund's net asset value, or diminish the fund's performance.    Municipal Securities Risk. Principal and interest payments on municipal securities may not be guaranteed by the issuing body and may be payable only from a particular source. That source may not perform as expected and payment obligations may not be made or made on time.    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. 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	No performance information is shown because the Fund has not yet had a calendar year of performance. The Fund's performance will be benchmarked against the Barclays Capital Municipal Bond Index.
Performance, One Year or Less	rr_PerformanceOneYearOrLess	No performance information is shown because the Fund has not yet had a calendar year of performance.
Opportunistic Municipal Fund (Prospectus Summary) | Opportunistic Municipal Fund | Class A
Risk Return [Abstract]	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	3.75%
Maximum Deferred Sales Charge (Load) (as a percentage of dollars subject to charge)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%
Management Fees	rr_ManagementFeesOverAssets	0.50%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.51%	[1],[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.26%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.29%)	[3]
Total Annual Fund Operating Expenses after Expense Reimbursement	rr_NetExpensesOverAssets	0.97%
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2013-12-31
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	470
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	732
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	470
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	732
Opportunistic Municipal Fund (Prospectus Summary) | Opportunistic Municipal Fund | Class C
Risk Return [Abstract]	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of dollars subject to charge)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%
Management Fees	rr_ManagementFeesOverAssets	0.50%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.54%	[1],[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.04%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.32%)	[3]
Total Annual Fund Operating Expenses after Expense Reimbursement	rr_NetExpensesOverAssets	1.72%
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2013-12-31
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	275
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	609
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	175
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	609

[1] Other Expenses are estimated for the year ending August 31, 2012.

[2] Other Expenses include: Interest Expense 0.07%

[3] Principal Management Corporation ("Principal"), the investment advisor, has contractually agreed to limit the Fund's expenses attributable to Class A and Class C shares and, if necessary, pay expenses normally payable by the Fund, excluding interest expense through the period ending December 31, 2013. 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 0.90% for Class A and 1.65% for Class C shares. 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.