Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA FUNDS SERIES TRUST I
Prospectus Date	rr_ProspectusDate	Mar. 10, 2017
Columbia Small Cap Value Fund I
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY OF THE FUND
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Columbia Small Cap Value Fund I (the Fund) seeks long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy Class T shares of the Fund. The front-end sales charge applicable to Class T shares is a per-transaction charge, meaning that separate orders will not be aggregated for purposes of calculating the rate of the sales charge payable. In addition to sales charge waivers made available to all Class T investors, certain financial intermediaries may offer their own (i.e., a financial intermediary-specific) sales charge waiver(s). More information about this is available in the Choosing a Share Class section beginning on page 18 of the Fund’s prospectus, which you should review carefully before investing.
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)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund may pay 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 65% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	65.00%
Expenses Restated to Reflect Current [Text]	rr_ExpensesRestatedToReflectCurrent	Other expenses are based on estimated amounts for the Fund’s current fiscal year.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following 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 illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that: you invest $10,000 in the class of Fund shares for the periods indicated, your investment has a 5% return each year, and the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal circumstances, the Fund invests at least 80% of its net assets (including the amount of any borrowings for investment purposes) in equity securities of companies that have market capitalizations in the range of the companies in the Russell 2000 Value Index (the Index) at the time of purchase (between $35.9 million and $10.6 billion as of December 31, 2016), that the Fund’s investment manager believes are undervalued. The market capitalization range and composition of the companies in the Index are subject to change. The Fund may invest up to 20% of its total assets in foreign securities. The Fund also may invest up to 20% of its total assets in real estate investment trusts. The Fund may from time to time emphasize one or more economic sectors in selecting its investments, including the financial services sector.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	An investment in the Fund involves risks, including those described below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Active Management Risk. Due to its active management, the Fund could underperform its benchmark index and/or other funds with similar investment objectives and/or strategies. Foreign Securities Risk. Investments in or exposure to foreign securities involve certain risks not associated with investments in or exposure to securities of U.S. companies. Foreign securities subject the Fund to the risks associated with investing in the particular country of an issuer, including the political, regulatory, economic, social, diplomatic and other conditions or events (including, for example, military confrontations, war and terrorism), occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies, and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. In addition, foreign governments may impose withholding or other taxes on the Fund’s income, capital gains or proceeds from the disposition of foreign securities, which could reduce the Fund’s return on such securities. The performance of the Fund may also be negatively impacted by fluctuations in a foreign currency's strength or weakness relative to the U.S. dollar, particularly to the extent the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar. Issuer Risk. An issuer in which the Fund invests or to which it has exposure may perform poorly, and the value of its securities may therefore decline, which would negatively affect the Fund’s performance. Poor performance may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters or other events, conditions or factors. Market Risk. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods. Real Estate-Related Investment Risk. Investments in real estate investment trusts (REITs) and in securities of other companies (wherever organized) principally engaged in the real estate industry subject the Fund to, among other things, risks similar to those of direct investments in real estate and the real estate industry in general. These include risks related to general and local economic conditions, possible lack of availability of financing and changes in interest rates or property values. REITs are entities that either own properties or make construction or mortgage loans, and also may include operating or finance companies. The value of interests in a REIT may be affected by, among other factors, changes in the value of the underlying properties owned by the REIT, changes in the prospect for earnings and/or cash flow growth of the REIT itself, defaults by borrowers or tenants, market saturation, decreases in market rates for rents, and other economic, political, or regulatory matters affecting the real estate industry, including REITs. REITs and similar non-U.S. entities depend upon specialized management skills, may have limited financial resources, may have less trading volume in their securities, and may be subject to more abrupt or erratic price movements than the overall securities markets. REITs are also subject to the risk of failing to qualify for favorable tax treatment under the Internal Revenue Code of 1986, as amended. Some REITs (especially mortgage REITs) are affected by risks similar to those associated with investments in debt securities including changes in interest rates and the quality of credit extended. Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within a sector, including the financial services sector. Companies in the same sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that sector than funds that invest more broadly. Generally, the more broadly the Fund invests, the more it spreads risk and potentially reduces the risks of loss and volatility. The Fund may be more susceptible to the particular risks that may affect companies in the financial services sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the financial services sector are subject to certain risks, including the risk of regulatory change, decreased liquidity in credit markets and unstable interest rates. Such companies may have concentrated portfolios, such as a high level of loans to real estate developers, which makes them vulnerable to economic conditions that affect that industry. Performance of such companies may be affected by competitive pressures and exposure to investments or agreements that, under certain circumstances, may lead to losses (e.g., subprime loans). Companies in the financial services sector are subject to extensive governmental regulation that may limit the amount and types of loans and other financial commitments they can make, and interest rates and fees that they may charge. In addition, profitability of such companies is largely dependent upon the availability and the cost of capital. Small Company Securities Risk. Investments in small-capitalization companies (small-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies, and securities of small-cap companies may be less liquid and more volatile than the securities of larger companies. Value Securities Risk. Value securities are securities of companies that may have experienced, for example, adverse business, industry or other developments or may be subject to special risks that have caused the securities to be out of favor and, in turn, potentially undervalued. The market value of a portfolio security may not meet portfolio management’s perceived value assessment of that security, or may decline in price, even though the portfolio manager(s) believe(s) the securities are already undervalued. There is also a risk that it may take longer than expected for the value of these investments to rise to portfolio management’s perceived value. In addition, value securities, at times, may not perform as well as growth securities or the stock market in general, and may be out of favor with investors for varying periods of time.
Risk Lose Money [Text]	rr_RiskLoseMoney	There is no assurance that the Fund will achieve its investment objective and you may lose money.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a bank deposit 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 Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. Class T shares of the Fund did not commence operations prior to the date of this prospectus and, therefore, performance information is not yet available. The bar chart shows how the Fund’s Class A share performance (without sales charges) has varied for each full calendar year shown. If the sales charges were reflected, returns shown would be lower. Class A shares are offered in a separate prospectus. The table below the bar chart compares the Fund’s returns (after applicable sales charges) for the periods shown with a broad measure of market performance. Any share class, such as Class T shares, that does not have available performance would have annual returns substantially similar to those of Class A shares. Except for differences in annual returns resulting from differences in expenses and sales charges (where applicable), the share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities. The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-advantaged accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes. The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedle.com/us.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class A share performance (without sales charges) has varied for each full calendar year shown. If the sales charges were reflected, returns shown would be lower. Class A shares are offered in a separate prospectus. The table below the bar chart compares the Fund’s returns (after applicable sales charges) for the periods shown with a broad measure of market performance.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	Class T shares of the Fund did not commence operations prior to the date of this prospectus and, therefore, performance information is not yet available.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800.345.6611
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	columbiathreadneedle.com/us
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Year by Year Total Return (%) as of December 31 Each Year
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	The bar chart shows how the Fund’s Class A share performance (without sales charges) has varied for each full calendar year shown. If the sales charges were reflected, returns shown would be lower.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best and Worst Quarterly Returns During the Period Shown in the Bar Chart Best                            3rd Quarter 2009                             20.59% Worst                          4th Quarter 2008                            -24.09%
Bar Chart, Returns for Class Not Offered in Prospectus [Text]	rr_BarChartReturnsForClassNotOfferedInProspectus	The bar chart shows how the Fund’s Class A share performance (without sales charges) has varied for each full calendar year shown. If the sales charges were reflected, returns shown would be lower. Class A shares are offered in a separate prospectus. Any share class, such as Class T shares, that does not have available performance would have annual returns substantially similar to those of Class A shares. Except for differences in annual returns resulting from differences in expenses and sales charges (where applicable), the share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities.
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2016)
Performance Table Does Reflect Sales Loads	rr_PerformanceTableDoesReflectSalesLoads	The table below the bar chart compares the Fund’s returns (after applicable sales charges) for the periods shown with a broad measure of market performance.
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates and do not reflect the impact of state, local or foreign taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	In addition, the after-tax returns shown in the table do not apply to shares held in tax-advantaged accounts such as 401(k) plans or Individual Retirement Accounts (IRAs).
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	The after-tax returns are shown only for Class A shares and will vary for other share classes.
Columbia Small Cap Value Fund I | Class T
Risk/Return:	rr_RiskReturnAbstract
Maximum sales charge (load) imposed on purchases (as a % of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	2.50%
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	rr_MaximumDeferredSalesChargeOverOther	none
Management fees	rr_ManagementFeesOverAssets	0.85%
Distribution and/or service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other expenses	rr_OtherExpensesOverAssets	0.25%	[1]
Total annual Fund operating expenses	rr_ExpensesOverAssets	1.35%
1 year	rr_ExpenseExampleYear01	$ 384
3 years	rr_ExpenseExampleYear03	667
5 years	rr_ExpenseExampleYear05	971
10 years	rr_ExpenseExampleYear10	1,833
1 year	rr_ExpenseExampleNoRedemptionYear01	384
3 years	rr_ExpenseExampleNoRedemptionYear03	667
5 years	rr_ExpenseExampleNoRedemptionYear05	971
10 years	rr_ExpenseExampleNoRedemptionYear10	$ 1,833
Columbia Small Cap Value Fund I | Class A
Risk/Return:	rr_RiskReturnAbstract
2007	rr_AnnualReturn2007	(2.63%)
2008	rr_AnnualReturn2008	(28.23%)
2009	rr_AnnualReturn2009	24.44%
2010	rr_AnnualReturn2010	25.72%
2011	rr_AnnualReturn2011	(6.24%)
2012	rr_AnnualReturn2012	11.11%
2013	rr_AnnualReturn2013	33.86%
2014	rr_AnnualReturn2014	2.84%
2015	rr_AnnualReturn2015	(6.48%)
2016	rr_AnnualReturn2016	32.32%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	20.59%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(24.09%)
1 Year	rr_AverageAnnualReturnYear01	24.72%
5 Years	rr_AverageAnnualReturnYear05	12.27%
10 Years	rr_AverageAnnualReturnYear10	6.22%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Jul. 25, 1986
Columbia Small Cap Value Fund I | returns after taxes on distributions | Class A
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	21.03%
5 Years	rr_AverageAnnualReturnYear05	9.27%
10 Years	rr_AverageAnnualReturnYear10	4.39%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Jul. 25, 1986
Columbia Small Cap Value Fund I | returns after taxes on distributions and sale of Fund shares | Class A
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	16.20%
5 Years	rr_AverageAnnualReturnYear05	9.24%
10 Years	rr_AverageAnnualReturnYear10	4.68%
Share Class Inception Date	rr_AverageAnnualReturnInceptionDate	Jul. 25, 1986
Columbia Small Cap Value Fund I | Russell 2000 Value Index (reflects no deductions for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	31.74%
5 Years	rr_AverageAnnualReturnYear05	15.07%
10 Years	rr_AverageAnnualReturnYear10	6.26%

[1] Other expenses are based on estimated amounts for the Fund’s current fiscal year.