Objective, Primary [Text Block]

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Risk/Return [Heading]

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GREEN CENTURY MSCI INTERNATIONAL INDEX FUND SUMMARY SECTION

Objective [Heading]

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Investment Objective

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The Green Century MSCI International Index Fund seeks to achieve long-term total return which matches the performance of an index comprised of the stocks of foreign companies selected based on environmental, social and governance (ESG) criteria.

Expense [Heading]

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Fees and Expenses of the Fund

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy, hold and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below. If you invest in shares of the Fund through an investment professional or financial intermediary, that investment professional or financial intermediary may charge you a commission in an amount determined and separately disclosed to you by that investment professional or financial intermediary.

Shareholder Fees Caption [Text]

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Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Text]

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Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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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 29% of the average value of its portfolio.

Portfolio Turnover, Rate

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29.00%

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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This example is intended to help you compare the costs of investing in the Fund with the cost of investing in other mutual funds. This example assumes that: (1) 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; (2) your investment has a 5%

return each year; and (3) 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:

Strategy [Heading]

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Principal Investment Strategies

Strategy Narrative [Text Block]

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The Fund invests substantially all of its assets in the common stocks which make up the MSCI World ex USA SRI ex Fossil Fuels Index (the World ex USA SRI ex Fossil Fuels Index or the Index), a custom index calculated by MSCI, Inc. The World ex USA SRI ex Fossil Fuels Index is comprised of the common stocks of the companies in the MSCI World ex USA SRI Index (the World ex USA SRI Index), minus the stocks of the companies that:

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Explore for, extract, produce, manufacture or refine coal, oil or gas;

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Produce or transmit electricity derived from fossil fuels or transmit natural gas;

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Have carbon reserves included in the World ex USA SRI (Socially Responsible Investment) Index.

The World ex USA SRI Index includes large and mid‑cap stocks from approximately 22 developed markets countries (excluding the U.S.). The World ex USA SRI Index is a capitalization weighted index that provides exposure to companies with what MSCI calculates to have high ESG ratings.

In constructing the World ex USA SRI Index, MSCI ESG Research analyzes a company’s commitment to sustainability across the following ESG issues that focus on the intersection between a company’s core business and the industry-specific issues that may create significant risks and opportunities for the company:

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Environmental issues, including:

Climate Change: carbon emissions; product carbon footprint; financing environmental impact; and climate change vulnerability.

Natural Capital: water stress; biodiversity and land use; and raw material sourcing.

Pollution and Waste: toxic emissions and waste; packaging material and waste; and electronic waste.

Environmental Opportunities: clean technology; green building; and renewable energy.

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Social issues, including:

Human Capital: labor management; health and safety; human capital development; and supply chain labor standards.

Product Liability: product safety and quality; chemical safety; financial product safety; privacy and data security; responsible investment; and insuring health and demographic risk.

Stakeholder Opposition: controversial sourcing.

Social Opportunities: access to communication; access to finance; access to health care; and opportunities in nutrition and health.

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Governance issues, including:

Corporate Governance: board; pay; ownership and accounting.

Corporate Behavior: business ethics; anti-competitive practices; corruption and instability; financial system instability; and tax transparency.]

MSCI ESG Research’s process in constructing the World ex USA SRI Index includes the identification of the above key issues by industry; measuring a company’s risk exposure for each key issue; and measuring a company’s risk management for each key issue.

Companies that MSCI ESG Research has determined to have significant business involvement in the following will not be included in the World ex USA SRI Index:

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Companies that are primarily engaged in the production of nuclear energy or the manufacture of nuclear equipment to produce nuclear energy or nuclear weapons, in the belief that these products are unacceptably threatening to a sustainable global environment.

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Companies that are primarily engaged in the manufacture of tobacco products, which are linked to air pollution, deforestation, and plastic pollution, as well as health problems.

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Companies that have a significant business involvement in genetically modified organisms (GMOs) whose use has led to increased use of toxic herbicides.

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Companies that are in industries that produce firearms or military weapons.

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Companies that are primarily engaged in gambling, alcohol or adult entertainment

Green Century believes that constructing a Fund’s portfolio based on ESG criteria creates an incentive for companies to become more sustainable. Green Century believes that those companies which seek to manage their ESG risks may be better prepared to avoid reputational, competitive, regulatory and material risks and may benefit financially as a result. Green Century also believes that the growing use of ESG ratings may create an incentive for companies to measure and manage their risks better to secure higher scores on ESG ratings systems.

The Fund buys and sells stocks so that the composition of its securities holdings will correspond, to the extent reasonably practicable, to the composition of securities in the World ex USA SRI ex Fossil Fuels Index. The weightings of the stocks in the World ex USA SRI ex Fossil Fuels Index are based on float-adjusted market capitalizations, which means the largest companies comprise a higher percentage of the World ex USA SRI ex Fossil Fuels Index and the Index is more heavily weighted in large than in smaller companies. As of September 30, 2022, the World ex USA SRI ex Fossil Fuels Index included companies with market capitalizations between approximately $2 billion and $194 billion. To the extent practicable, the Fund will seek a correlation between the weightings of securities held by the Fund and the weightings of the securities

of the World ex USA SRI ex Fossil Fuels Index of 0.95 or better. A figure of 1.00 would indicate a perfect correlation. The Fund’s ability to duplicate the performance of the World ex USA SRI ex Fossil Fuels Index will depend to some extent on the size and timing of cash flows into and out of the Fund as well as the Fund’s expenses.

Under normal circumstances and as a matter of operating policy, the Fund will invest at least 80% of its assets in the component securities of the World ex USA SRI ex Fossil Fuels Index and may invest in American Depository Receipts, Global Depository Receipts and Euro Depository Receipts representing the component securities of the Index.

Risk [Heading]

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Principal Risks

Risk Narrative [Text Block]

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You may lose money by investing in the Fund. As with any mutual fund, there can be no guarantee that the Fund will achieve its objective. The following is a summary description of certain risks of investing in the Fund:

Market Risk. The market prices of securities or other assets held by the Fund may fall, sometimes rapidly or unpredictably, due to general market conditions, such as real or perceived adverse economic or political conditions, recessions, inflation, changes in interest or currency rates, lack of liquidity in the bond markets, the spread of infectious illness or other public health issues, armed conflict, market disruptions caused by tariffs, trade disputes, sanctions or other government actions, or other factors, or adverse investor sentiment. If the market prices of the Fund’s securities and assets fall, the value of your investment will go down. A change in financial condition or other event affecting a single issuer may adversely impact securities markets as a whole. Rates of inflation have recently risen. The value of assets or income from an investment may be worth less in the future as inflation decreases the value of money. As inflation increases, the real value of the Fund’s assets can decline as can the value of the Fund’s distributions.

Changes in market conditions will not typically have the same impact on all types of securities. The market prices of securities may fall due to factors affecting a particular issuer, industry or the securities market as a whole. In the past decade, financial markets throughout the world have experienced increased volatility, depressed valuations, decreased liquidity and heightened uncertainty. Governmental and non‑ governmental issuers have defaulted on, or been forced to restructure, their debts. These conditions may continue, recur, worsen or spread. Events that have contributed to these market conditions include, but are not limited to major cybersecurity events; geopolitical events (including wars, terror attacks and economic sanctions); measures to address budget deficits; downgrading of sovereign debt; changes in oil and commodity prices; dramatic changes in currency exchange rates; global pandemics; and public sentiment. The global pandemic of the novel coronavirus respiratory disease designated COVID‑19 has resulted in major disruption to economies and markets around the world, including the United States. Global financial markets have experienced extreme volatility and severe losses, and trading in many instruments has been disrupted. Liquidity for many instruments has been greatly reduced for periods of time. Some sectors of the economy and individual issuers have experienced particularly large losses. These circumstances may continue for an extended period of time, and may continue to affect adversely the value and liquidity of the Fund’s investments. Following Russia’s invasion of Ukraine, Russian securities have lost all, or nearly all, their market value. Other securities or markets could be similarly affected by past or future geopolitical or other events or conditions.

Governments and central banks, including the U.S. Federal Reserve, have taken extraordinary and unprecedented actions to support local and global economies and the financial markets. These actions have resulted in significant expansion of public debt, including in the U.S. The consequences of high public debt, including its future impact on the economy and securities markets, may not be known for some time. Although they have started to increase, interest rates are still very low, which means there is more risk that they may go up. U.S. Federal Reserve or other U.S. or non‑U.S. governmental or central bank actions, including increases or decreases in interest rates, or contrary actions by different governments could negatively affect financial markets generally, increase market volatility and reduce the value and liquidity of securities in which the Fund invests. Policy and legislative changes in the United States and in other countries are affecting many aspects of financial regulation and these and other events affecting global markets, such as the United Kingdom’s exit from the European Union (or Brexit), potential trade imbalances with China or other countries, or sanctions or other government actions against Russia, other nations or individuals or companies (or their countermeasures), may in some instances contribute to decreased liquidity and increased volatility in the financial markets. The impact of these changes on the markets, and the practical implications for market participants, may not be fully known for some time.

Economies and financial markets throughout the world are increasingly interconnected. Economic, financial or political events, trading and tariff arrangements, armed conflict including Russia’s military invasion of Ukraine, terrorism, natural disasters, infectious illness or public health issues, cybersecurity events, supply chain disruptions, sanctions against Russia, other nations or individuals or companies and possible countermeasures, and other circumstances in one country or region could have profound impacts on other countries or regions and on global economies or markets. As a result, whether or not the Fund invests in securities of issuers located in or with significant exposure to the countries or regions directly affected, the value and liquidity of the Fund’s investments may be negatively affected.

Environmental, Social and Governance Investing Risk. The Fund’s environmental, social and governance criteria limit the available investments compared with funds with no such criteria. Under certain economic conditions, this could cause the Fund’s investment performance to be worse or better than similar funds with no such criteria.

Equity Securities Risk. The Fund is heavily invested in stocks. Like all funds invested in stocks, the Fund’s share price will fluctuate daily depending on the performance of the companies that comprise the Fund’s investments, the general market and the economy overall. After you invest, the value of your shares may be less than what you paid for them.

Large Cap Companies Risk. Large‑cap companies may be unable to respond quickly to new competitive challenges such as changes in technology, and also may not be able to attain the high growth rate of successful smaller companies, especially during extended periods of economic expansion. The large‑cap companies in which the Fund invests may perform worse than the stock market as a whole.

Mid‑Cap Companies Risk. The Fund may be invested in mid‑cap companies which involve greater risk than investing in the stocks of larger, more established companies. Mid‑cap companies may lack the management experience, financial resources and product diversification of large companies and the frequency and volume of their trading may be less than that of larger companies. Therefore, securities of mid‑cap companies may be subject to wider and more erratic price fluctuations. Compared to large‑cap companies,

small‑cap and mid‑cap companies, and the market for their equity securities, may be more sensitive to changes in earnings results and investor expectations or poor economic or market conditions, including those experienced during a recession, experience sharper swings in market values, have limited liquidity, be harder to value or to sell at the times and prices the Subadviser thinks appropriate, and offer greater potential for gain and loss.

Risks of Non‑U.S. Investments. Investing in non‑U.S. issuers or in securities of U.S. issuers with significant exposure to foreign markets may involve unique risks compared to investing in securities of U.S. issuers. These risks are more pronounced to the extent that the Fund invests significantly in one region or country. These risks may include different financial reporting practices and regulatory standards, less liquid trading markets, currency risks, changes in economic, political, regulatory and social conditions, armed conflict including Russia’s military invasion of Ukraine, and sanctions or other government actions against Russia, other nations or individuals or companies (or their countermeasures), sustained economic downturns, reduction of government or central bank support, inadequate accounting standards, tariffs, tax disputes or other tax burdens, natural disasters, terrorism, nationalization or expropriation of assets, arbitrary application of laws and regulations or lack of rule of law, and investment and repatriation restrictions. Emerging market economies tend to be less diversified than those of more developed countries. They typically have fewer medical and economic resources than more developed countries and thus they may be less able to control or mitigate the effects of a pandemic.

Country Risk. The Fund expects to diversify its investments among issuers with significant exposure to various countries throughout the world but it may hold a large number of securities whose issuers have exposure to a single country, including but not limited to Japan, France, Germany, Canada, Switzerland and the United Kingdom (the “U.K.”). Significant exposure to a single country would increase the risk that economic, political, and social conditions in that country will have a significant impact on Fund performance.

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The Japanese economy is highly dependent upon international trade, particularly with the United States and other Asian countries. Because of its trade dependence, the Japanese economy is particularly exposed to the risks of currency fluctuation, foreign trade policy and regional and global economic disruption. In the past, Japan’s economic growth rate has remained relatively low, and it may remain low in the future. The Japanese economic growth rate could be impacted by Bank of Japan monetary policies, rising interest rates, tax increases, budget deficits, consumer confidence and volatility in the Japanese yen. Japan’s economy has been adversely affected by trade tariffs, other protectionist measures, competition from emerging economies and the economic conditions of trading partners. Strained foreign relations with neighboring countries (China, South Korea, North Korea and Russia) may not only negatively impact the Japanese economy but also the geographic region as well as globally. Economic growth in Japan is heavily dependent on continued growth in international trade, government support of the financial services sector, among other troubled sectors, and consistent government policy. In addition, the Japanese economy has been adversely affected by certain structural issues, including an aging population, significant non‑performing loan portfolios at major financial institutions, substantial government deficits, low domestic consumption and natural and environmental disasters.

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The French economy, including demand for French exports, may be adversely affected by the U.K.’s withdrawal from the European Union (“EU”). As a result, the French economy may experience

adverse trends due to concerns about a prolonged economic downturn, potential weakness in exports, high rates of unemployment and rising government debt levels. The French economy is dependent on agricultural exports, and as a result, is susceptible to fluctuations in demand for agricultural products. France has experienced several terrorist attacks in the past several years.

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Germany has an industrial and export dependent economy and relies heavily on trade with key trading partners, including the Netherlands, China, the U.S., the U.K., France, Italy and other European countries. Changes in the price or demand for German exports may have an adverse impact on Germany’s economy. In addition, heavy regulation of labor, energy and product markets in Germany may have an adverse impact on German issuers. Such regulations may negatively impact economic growth or cause prolonged periods of recession. Ongoing concerns regarding the economic health of the EU have negatively impacted the earnings of German financial services companies.

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The U.K. has one of the largest economies in Europe, and the U.S. and other European countries are substantial trading partners of the U.K. As a result, the U.K.’s economy may be impacted by changes to the economic condition of the U.S. and other European countries. The U.K.’s economy will also be significantly affected by the U.K.’s exit from the EU. The precise impact on the U.K’s economy as a result of its departure from the EU depends to a large degree on its ability to conclude favorable trade deals with the EU and other countries and offset the increased costs of trade resulting from the U.K.’s loss of its membership in the EU single market. Therefore, uncertainty remains as to the long-term consequences of Brexit

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The Canadian economy is heavily dependent on relationships with certain key trading partners, including the U.S. and China. The Canadian economy is sensitive to fluctuations in certain commodity markets.

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International trade is a large component of the Swiss economy and Switzerland depends upon exports to generate economic growth. The Swiss economy relies on certain key trading partners including the United States, Europe and China. Switzerland’s economic growth is generally correlated to slowdowns and growth trends experienced in other countries, including the U.S. and certain Western European countries.

Market Sector Risk. The Fund may hold a large percentage of securities in a single market sector. To the extent the Fund holds a large percentage of securities in a single sector, its performance will be tied closely to and affected by the performance of that sector, and the Fund will be subject to a greater degree to any market price movements, regulatory or technological change, economic conditions or other developments or risks affecting such market sector than a fund without the same focus.

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Financial Sector Risk. Issuers in the financial sector, such as banks, insurance companies and broker- dealers, may be sensitive to changes in interest rates, credit rating downgrades, decreased liquidity in credit markets, and general economic activity and are generally subject to extensive government regulation.

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Technology Sector Risk. Securities in the technology sector, such as information technology, communications equipment, computer hardware and software, and office and scientific equipment, are generally subject to risks of rapidly evolving technology, short product lives, rates of corporate expenditures, falling prices and profits, competition from new market entrants, and general economic conditions. They are also heavily dependent on intellectual property rights and may be adversely affected by the loss or impairment of, or inability to enforce, those rights.

Liquidity Risk. Liquidity risk exists when particular investments are difficult to purchase or sell. When the Fund holds these types of investments, the Fund’s portfolio may be more difficult to value, especially during periods of market turmoil or due to adverse changes in the conditions of a particular issuer. Markets may become illiquid when there are few, if any, interested buyers or sellers or when dealers are unwilling or unable to make a market for certain securities. As a general matter, dealers recently have been less willing to make markets for fixed income securities or when dealer market-making capacity is otherwise reduced. During times of market turmoil, there have been, and may be, no buyers for securities in entire asset classes, including U.S. Treasury securities. When the Fund holds illiquid investments, the Fund may be harder to value, especially in changing markets. Investments by the Fund in below investment grade securities, foreign securities, and corporate loans tend to involve greater liquidity risk. If the Fund is forced to sell or unwind these investments to meet redemptions or for other cash needs or try to limit losses, the Fund may suffer a substantial loss or may not be able to sell at all. Additionally, the market for certain investments may become illiquid under adverse market or economic conditions independent of any specific adverse changes in the conditions of a particular issuer. In such cases, the Fund, due to limitations on investments in illiquid securities and the difficulty in purchasing and selling such securities, may be unable to achieve its desired level of exposure to certain sectors. Further, certain securities, once sold, may not settle for an extended period. The Fund will not receive its sales proceeds until that time, which may constrain the Fund’s ability to meet its obligations (including obligations to redeeming shareholders).

Index Fund Risk. The Fund will invest in the stocks composing the World ex USA SRI ex Fossil Fuels Index regardless of how the Index is performing. It will not shift concentration from one industry to another, or from stocks to bonds or cash, in order to defend against a falling stock market. The Index may, at times, become focused in stocks of a particular sector, category or group of companies. Because the Fund seeks to track the World ex USA SRI ex Fossil Fuels Index, the Fund may underperform the overall stock market.

Non-Correlation Risk. The performance of the Fund and of the World ex USA SRI ex Fossil Fuels Index may vary for a variety of reasons. For example, the Fund incurs operating expenses and portfolio transaction costs not incurred by the Index. In addition, the Fund may not be fully invested in the component securities of the Index.

Valuation Risk. Nearly all of the Fund’s securities are valued using a fair value methodology. The sales price the Fund could receive for any particular portfolio investment may differ from the Fund’s valuation of the investment, particularly for securities that trade in thin or volatile markets. These differences may increase significantly and affect Fund investments more broadly during periods of market volatility. Investors who purchase or redeem Fund shares may receive fewer or more shares or lower or higher redemption proceeds than they would have received if the Fund had not fair-valued securities or had used a different valuation methodology. The Fund’s ability to value its investments may be impacted by technological issues and/or errors by pricing services or other third party service providers.

Redemption Risk. The Fund may experience periods of heavy redemptions that could cause the Fund to liquidate its assets at inopportune times or at a loss or depressed value, particularly during periods of declining or illiquid markets. Redemption risk is greater to the extent that the Fund has investors with large shareholdings, short investment horizons, or unpredictable cash flow needs. In addition, redemption risk is heightened during periods of overall market turmoil. The redemption by one or more large shareholders of

their holdings in the Fund could hurt performance and/or cause the remaining shareholders in the Fund to lose money. Further, if one decision maker has control of Fund shares owned by separate Fund shareholders, including clients or affiliates of the Fund’s Adviser, redemptions by these shareholders may further increase the Fund’s redemption risk. If the Fund is forced to liquidate its assets under unfavorable conditions or at inopportune times, the value of your investment could decline.

Cybersecurity Risk. Cybersecurity failures by or breaches of the Fund’s Adviser, Subadviser, transfer agent, distributor, custodian, fund accounting agent or other service providers may disrupt Fund operations, interfere with the Fund’s ability to calculate its NAV, prevent Fund shareholders from purchasing, redeeming or exchanging shares or receiving distributions or receiving timely information regarding the Fund or their investment in the Fund, cause loss of or unauthorized access to private shareholder information, and result in financial losses to the Fund and its shareholders, regulatory fines, penalties, reputational damage, or additional compliance costs. Substantial costs may be incurred in order to prevent any cyber incidents in the future. The Fund and its shareholders could be negatively impacted as a result.

These and other risks are discussed in more detail in “Additional Information About the Funds’ Investment Objectives, Strategies and Risks” in this Prospectus and in the Statement of Additional Information.

Risk Lose Money [Text]

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You may lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

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Performance

Performance Narrative [Text Block]

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The bar chart and the average annual total return table below provide some indication of the risks of investing in the Fund by showing how the Fund has performed in the past. The bar chart shows changes in the performance of the Fund’s Individual Investor Class from year to year. The table shows how the average annual total return for each class of the Fund for the 1 and 5 year periods and since inception periods compare with the returns of a broad measure of market performance.

The Fund’s past performance (before and after taxes) does not necessarily indicate how well it will perform in the future. Updated performance information is available on the Fund’s website, www.greencentury.com/fund-performance/, or by calling 1‑800‑934‑7336.

Performance Information Illustrates Variability of Returns [Text]

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Performance Availability Phone [Text]

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1‑800‑934‑7336

Performance Availability Website Address [Text]

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www.greencentury.com/fund-performance/

Performance Past Does Not Indicate Future [Text]

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The Fund’s past performance (before and after taxes) does not necessarily indicate how well it will perform in the future.

Bar Chart [Heading]

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Annual Total Return for the Year Ended December 31 Green Century MSCI International Index Fund – Individual Investor Class

Bar Chart Closing [Text Block]

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During the period shown, the best quarterly performance of the Fund’s Individual Investor Class was 15.68%, for the quarter ended 6/30/20. The worst quarterly performance of the Fund’s Individual Investor Class was -19.51%, for the quarter ended 3/31/20.

As of September 30, 2022, the year‑to‑date return for the Fund’s Individual Investor Class was -32.45%.

Performance Table Heading

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Average Annual Total Returns for the Periods Ended December 31, 2021

Performance Table Uses Highest Federal Rate

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The 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

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Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

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The after-tax returns are shown for the Individual Investor Class of the Fund and the after-tax returns for the Institutional Class of the Fund will vary.

Performance Table Narrative

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The after-tax returns are shown for the Individual Investor Class of the Fund and the after-tax returns for the Institutional Class of the Fund will vary. The 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. After-tax returns are not relevant to investors who hold their Fund shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts.

Green Century MSCI International Index Fund | Individual Investor Class

Maximum Sales Charge (Load) Imposed on Purchases

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none

Maximum Deferred Sales Charge (Load)

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none

Redemption Fee (as a percentage of an amount redeemed within 60 days of purchase)

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2.00%

Wire Redemption Fee (if such services are requested)

gcf_WireRedemptionFeeIfSuchServicesAreRequested

$ 10

Overnight Delivery Fee (if such services are requested)

gcf_OvernightDeliveryFeeIfSuchServicesAreRequested

$ 30

Management Fees

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0.28%

Distribution (12b-1) Fees

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none

Administrative Fees

rr_Component1OtherExpensesOverAssets

1.00%

Other Fees

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none

Total Annual Fund Operating Expenses

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1.28%

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$ 130

3 Years

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406

Year to Date Return, Label

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702

10 Years

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$ 1,545

2017

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23.85%

2018

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(14.33%)

2019

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25.02%

2020

rr_AnnualReturn2020

12.17%

2021

rr_AnnualReturn2021

12.54%

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year‑to‑date return

Bar Chart, Year to Date Return, Date

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Sep. 30, 2022

Bar Chart, Year to Date Return

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(32.45%)

Highest Quarterly Return, Label

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best quarterly performance

Highest Quarterly Return, Date

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Jun. 30, 2020

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

15.68%

Lowest Quarterly Return, Label

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worst quarterly performance

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Mar. 31, 2020

Lowest Quarterly Return

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(19.51%)

rr_AverageAnnualReturnYear01

12.54%

rr_AverageAnnualReturnYear05

10.86%

rr_AverageAnnualReturnSinceInception

9.67%

Green Century MSCI International Index Fund | Institutional Class

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2016

Maximum Sales Charge (Load) Imposed on Purchases

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none

Maximum Deferred Sales Charge (Load)

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none

Redemption Fee (as a percentage of an amount redeemed within 60 days of purchase)

rr_RedemptionFeeOverRedemption

2.00%

Wire Redemption Fee (if such services are requested)

gcf_WireRedemptionFeeIfSuchServicesAreRequested

$ 10

Overnight Delivery Fee (if such services are requested)

gcf_OvernightDeliveryFeeIfSuchServicesAreRequested

$ 30

Management Fees

rr_ManagementFeesOverAssets

0.28%

Distribution (12b-1) Fees

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none

Administrative Fees

rr_Component1OtherExpensesOverAssets

0.70%

Other Fees

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none

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.98%

rr_ExpenseExampleYear01

$ 100

3 Years

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312

rr_ExpenseExampleYear05

542

10 Years

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$ 1,201

rr_AverageAnnualReturnYear01

12.90%

rr_AverageAnnualReturnYear05

11.19%

rr_AverageAnnualReturnSinceInception

9.98%

Green Century MSCI International Index Fund | Return after taxes on distributions | Individual Investor Class

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2016

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rr_AverageAnnualReturnYear01

11.77%

rr_AverageAnnualReturnYear05

10.42%

rr_AverageAnnualReturnSinceInception

9.24%

Green Century MSCI International Index Fund | Return after taxes on distributions and sale of Fund shares | Individual Investor Class

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2016

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rr_AverageAnnualReturnYear01

7.97%

rr_AverageAnnualReturnYear05

8.57%

rr_AverageAnnualReturnSinceInception

7.61%

Green Century MSCI International Index Fund | MSCI World Ex USA Index (reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2016

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

12.62%

rr_AverageAnnualReturnYear05

9.63%

rr_AverageAnnualReturnSinceInception

9.07%