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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Jul. 31, 2011
Registrant Name dei_EntityRegistrantName GEORGE PUTNAM FUND OF BOSTON
Central Index Key dei_EntityCentralIndexKey 0000081259
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Nov. 25, 2011
Document Effective Date dei_DocumentEffectiveDate Nov. 30, 2011
Prospectus Date rr_ProspectusDate Nov. 30, 2011
George Putnam Balanced Fund
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund summary
Objective [Heading] rr_ObjectiveHeading Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock George Putnam Balanced Fund seeks to provide a balanced investment composed of a well-diversified portfolio of stocks and bonds which produce both capital growth and current income.
Fees and expenses gpfob81259_FundFeesAndExpensesAbstract  
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses 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 $50,000 in Putnam funds. More information about these and other discounts is available from your financial advisor and in How do I buy fund shares? beginning on page 15 of the fund’s prospectus and in How to buy shares beginning on page II-1 of the fund’s statement of additional information (SAI).
Expense Breakpoint Discounts gpfob81259_ExpenseBreakpointDiscountsAbstract  
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Putnam funds. More information about these and other discounts is available from your financial advisor and in How do I buy fund shares? beginning on page 15 of the fund’s prospectus and in How to buy shares beginning on page II-1 of the fund’s statement of additional information (SAI).
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount 50,000
Shareholder fees rr_ShareholderFeesAbstract  
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder fees (fees paid directly from your investment)
Annual fund operating expenses rr_OperatingExpensesAbstract  
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual fund operating expenses (expenses you pay each year as a percentage of the value of your investment)
Expense Example rr_ExpenseExampleAbstract  
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. It assumes that you invest $10,000 in the fund for the time periods indicated and then, except as indicated, redeem all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Portfolio turnover gpfob81259_PortfolioTurnoverAltAbstract  
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The fund pays transaction-related costs when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs and may result in higher taxes when the fund’s shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 176%.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 176.00%
Strategy [Heading] rr_StrategyHeading Investments
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock We (Putnam Investment Management, LLC) invest mainly in a combination of bonds and U.S. value stocks with a greater focus on value stocks. Value stocks are those that we believe are currently undervalued by the market. If we are correct and other investors ultimately recognize the value of the company, the price of its stock may rise. Our equity investments are mainly those in large companies, which are of a size similar to those in the Russell 1000 Value Index (which was composed of companies having a market capitalization between $635 million and $353 billion as of September 30, 2011) and midsize companies, which are of a size similar to those in the Russell Midcap Value Index (which was composed of companies having a market capitalization between $635 million and $17 billion as of September 30, 2011). We buy bonds of governments and private companies that are mostly investment-grade in quality with intermediate- to long-term maturities (three years or longer). We may consider, among other factors, a company’s valuation, financial strength, growth potential, competitive position in its industry, projected future earnings, cash flows and dividends when deciding whether to buy or sell equity investments, and, among other factors, credit, interest rate and prepayment risks, as well as general market conditions, when deciding whether to buy or sell fixed income investments. We may also use derivatives, such as futures, options, warrants and swap contracts, for both hedging and non-hedging purposes.
Strategy Portfolio Concentration [Text] rr_StrategyPortfolioConcentration We (Putnam Investment Management, LLC) invest mainly in a combination of bonds and U.S. value stocks with a greater focus on value stocks.
Risk [Heading] rr_RiskHeading Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

It is important to understand that you can lose money by investing in the fund.

The prices of stocks and bonds in the fund’s portfolio may fall or fail to rise over extended periods of time for a variety of reasons, including both general financial market conditions and factors related to a specific company or industry. These risks are generally greater for small and midsize companies. Value stocks may fail to rebound, and the market may not favor value-style investing. The risks associated with bond investments include interest rate risk, which means the prices of the fund’s investments are likely to fall if interest rates rise. Bond investments are also subject to credit risk, which is the risk that the issuer of the fund’s investment may default on payment of interest or principal. Our use of derivatives may increase these risks by, for example, increasing investment exposure or, in the case of many over-the-counter instruments, because of the potential inability to terminate or sell derivatives positions.

The fund may not achieve its goal, and it is not intended to be a complete investment program. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text] rr_RiskLoseMoney It is important to understand that you can lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Performance gpfob81259_FundPastPerformanceAbstract  
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time. The bar chart does not reflect the impact of sales charges. If it did, performance would be lower. Please remember that past performance is not necessarily an indication of future results. Monthly performance figures for the fund are available at putnam.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information below gives some indication of the risks associated with an investment in the fund by showing the fund’s performance year to year and over time.
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The bar chart does not reflect the impact of sales charges. If it did, performance would be lower.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please remember that past performance is not necessarily an indication of future results.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock Monthly performance figures for the fund are available at putnam.com.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress putnam.com
Annual Total Returns rr_BarChartTableAbstract  
Bar Chart [Heading] rr_BarChartHeading Annual total returns for class A shares before sales charges
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Year-to-date performance

through 9/30/11

-4.44%

Best calendar quarter

Q2 2009

12.57%

Worst calendar quarter

Q4 2008

-26.96%
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-date performance through
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Sep. 30, 2011
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn (4.44%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best calendar quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 12.57%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst calendar quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (26.96%)
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Caption rr_AverageAnnualReturnCaption Average annual total returns after sales charges (for periods ending 12/31/10)
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock

The George Putnam Blended Index is an unmanaged index administered by Putnam Investment Management, LLC, 60% of which is the Russell 1000 Value Index and 40% of which is the Barclays Capital U.S. Aggregate Bond Index.

After-tax returns reflect the historical highest individual federal marginal income tax rates and do not reflect 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 shown for class A shares only and will vary for other classes. These after-tax returns do not apply if you hold your fund shares through a 401(k) plan, an IRA, or another tax-advantaged arrangement.

Class B share performance does not reflect conversion to class A shares.
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns reflect the historical highest individual federal marginal income tax rates and do not reflect 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.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns are shown for class A shares only and will vary for other classes.
George Putnam Balanced Fund | Class A
  
Shareholder fees rr_ShareholderFeesAbstract  
Share class rr_ShareholderFeesColumnName Class A
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice 1.00% [1]
Annual fund operating expenses rr_OperatingExpensesAbstract  
Share class rr_OperatingExpensesColumnName Class A
Management fees rr_ManagementFeesOverAssets 0.53%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.27%
Total annual fund operating expenses rr_ExpensesOverAssets 1.05%
Expense Example rr_ExpenseExampleAbstract  
Share class rr_ExpenseExampleByYearColumnName Class A
1 year rr_ExpenseExampleYear01 676
3 years rr_ExpenseExampleYear03 890
5 years rr_ExpenseExampleYear05 1,121
10 years rr_ExpenseExampleYear10 1,784
Annual Total Returns rr_BarChartTableAbstract  
2001 rr_AnnualReturn2001 0.51%
2002 rr_AnnualReturn2002 (8.42%)
2003 rr_AnnualReturn2003 17.39%
2004 rr_AnnualReturn2004 8.32%
2005 rr_AnnualReturn2005 4.04%
2006 rr_AnnualReturn2006 12.25%
2007 rr_AnnualReturn2007 0.92%
2008 rr_AnnualReturn2008 (40.30%)
2009 rr_AnnualReturn2009 25.80%
2010 rr_AnnualReturn2010 11.15%
George Putnam Balanced Fund | Class B
  
Shareholder fees rr_ShareholderFeesAbstract  
Share class rr_ShareholderFeesColumnName Class B
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 original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice 5.00% [2]
Annual fund operating expenses rr_OperatingExpensesAbstract  
Share class rr_OperatingExpensesColumnName Class B
Management fees rr_ManagementFeesOverAssets 0.53%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.27%
Total annual fund operating expenses rr_ExpensesOverAssets 1.80%
Expense Example rr_ExpenseExampleAbstract  
Share class rr_ExpenseExampleByYearColumnName Class B
1 year rr_ExpenseExampleYear01 683
3 years rr_ExpenseExampleYear03 866
5 years rr_ExpenseExampleYear05 1,175
10 years rr_ExpenseExampleYear10 1,919
Expense Example, No Redemption rr_ExpenseExampleNoRedemptionAbstract  
Share class rr_ExpenseExampleNoRedemptionByYearColumnName Class B (no redemption)
1 year rr_ExpenseExampleNoRedemptionYear01 183
3 years rr_ExpenseExampleNoRedemptionYear03 566
5 years rr_ExpenseExampleNoRedemptionYear05 975
10 years rr_ExpenseExampleNoRedemptionYear10 1,919
George Putnam Balanced Fund | Class C
  
Shareholder fees rr_ShareholderFeesAbstract  
Share class rr_ShareholderFeesColumnName Class C
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 original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice 1.00% [3]
Annual fund operating expenses rr_OperatingExpensesAbstract  
Share class rr_OperatingExpensesColumnName Class C
Management fees rr_ManagementFeesOverAssets 0.53%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.27%
Total annual fund operating expenses rr_ExpensesOverAssets 1.80%
Expense Example rr_ExpenseExampleAbstract  
Share class rr_ExpenseExampleByYearColumnName Class C
1 year rr_ExpenseExampleYear01 283
3 years rr_ExpenseExampleYear03 566
5 years rr_ExpenseExampleYear05 975
10 years rr_ExpenseExampleYear10 2,116
Expense Example, No Redemption rr_ExpenseExampleNoRedemptionAbstract  
Share class rr_ExpenseExampleNoRedemptionByYearColumnName Class C (no redemption)
1 year rr_ExpenseExampleNoRedemptionYear01 183
3 years rr_ExpenseExampleNoRedemptionYear03 566
5 years rr_ExpenseExampleNoRedemptionYear05 975
10 years rr_ExpenseExampleNoRedemptionYear10 2,116
George Putnam Balanced Fund | Class M
  
Shareholder fees rr_ShareholderFeesAbstract  
Share class rr_ShareholderFeesColumnName Class M
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 3.50%
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice 0.65% [1]
Annual fund operating expenses rr_OperatingExpensesAbstract  
Share class rr_OperatingExpensesColumnName Class M
Management fees rr_ManagementFeesOverAssets 0.53%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.75%
Other expenses rr_OtherExpensesOverAssets 0.27%
Total annual fund operating expenses rr_ExpensesOverAssets 1.55%
Expense Example rr_ExpenseExampleAbstract  
Share class rr_ExpenseExampleByYearColumnName Class M
1 year rr_ExpenseExampleYear01 502
3 years rr_ExpenseExampleYear03 822
5 years rr_ExpenseExampleYear05 1,165
10 years rr_ExpenseExampleYear10 2,131
George Putnam Balanced Fund | Class R
  
Shareholder fees rr_ShareholderFeesAbstract  
Share class rr_ShareholderFeesColumnName Class R
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 original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Annual fund operating expenses rr_OperatingExpensesAbstract  
Share class rr_OperatingExpensesColumnName Class R
Management fees rr_ManagementFeesOverAssets 0.53%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other expenses rr_OtherExpensesOverAssets 0.27%
Total annual fund operating expenses rr_ExpensesOverAssets 1.30%
Expense Example rr_ExpenseExampleAbstract  
Share class rr_ExpenseExampleByYearColumnName Class R
1 year rr_ExpenseExampleYear01 132
3 years rr_ExpenseExampleYear03 412
5 years rr_ExpenseExampleYear05 713
10 years rr_ExpenseExampleYear10 1,568
George Putnam Balanced Fund | Class Y
  
Shareholder fees rr_ShareholderFeesAbstract  
Share class rr_ShareholderFeesColumnName Class Y
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 original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Annual fund operating expenses rr_OperatingExpensesAbstract  
Share class rr_OperatingExpensesColumnName Class Y
Management fees rr_ManagementFeesOverAssets 0.53%
Distribution and service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets   
Other expenses rr_OtherExpensesOverAssets 0.27%
Total annual fund operating expenses rr_ExpensesOverAssets 0.80%
Expense Example rr_ExpenseExampleAbstract  
Share class rr_ExpenseExampleByYearColumnName Class Y
1 year rr_ExpenseExampleYear01 82
3 years rr_ExpenseExampleYear03 255
5 years rr_ExpenseExampleYear05 444
10 years rr_ExpenseExampleYear10 990
George Putnam Balanced Fund | before taxes | Class A
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Share class rr_AverageAnnualReturnColumnName Class A
Label rr_AverageAnnualReturnLabel before taxes
1 year rr_AverageAnnualReturnYear01 4.73%
5 years rr_AverageAnnualReturnYear05 (2.27%)
10 years rr_AverageAnnualReturnYear10 0.82%
George Putnam Balanced Fund | before taxes | Class B
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Share class rr_AverageAnnualReturnColumnName Class B
Label rr_AverageAnnualReturnLabel before taxes
1 year rr_AverageAnnualReturnYear01 5.28%
5 years rr_AverageAnnualReturnYear05 (2.17%)
10 years rr_AverageAnnualReturnYear10 0.65%
George Putnam Balanced Fund | before taxes | Class C
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Share class rr_AverageAnnualReturnColumnName Class C
Label rr_AverageAnnualReturnLabel before taxes
1 year rr_AverageAnnualReturnYear01 9.35%
5 years rr_AverageAnnualReturnYear05 (1.84%)
10 years rr_AverageAnnualReturnYear10 0.67%
George Putnam Balanced Fund | before taxes | Class M
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Share class rr_AverageAnnualReturnColumnName Class M
Label rr_AverageAnnualReturnLabel before taxes
1 year rr_AverageAnnualReturnYear01 6.77%
5 years rr_AverageAnnualReturnYear05 (2.29%)
10 years rr_AverageAnnualReturnYear10 0.57%
George Putnam Balanced Fund | before taxes | Class R
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Share class rr_AverageAnnualReturnColumnName Class R
Label rr_AverageAnnualReturnLabel before taxes
1 year rr_AverageAnnualReturnYear01 10.89%
5 years rr_AverageAnnualReturnYear05 (1.33%)
10 years rr_AverageAnnualReturnYear10 1.18%
George Putnam Balanced Fund | before taxes | Class Y
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Share class rr_AverageAnnualReturnColumnName Class Y
Label rr_AverageAnnualReturnLabel before taxes
1 year rr_AverageAnnualReturnYear01 11.39%
5 years rr_AverageAnnualReturnYear05 (0.86%)
10 years rr_AverageAnnualReturnYear10 1.68%
George Putnam Balanced Fund | after taxes on distributions | Class A
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Share class rr_AverageAnnualReturnColumnName Class A
Label rr_AverageAnnualReturnLabel after taxes on distributions
1 year rr_AverageAnnualReturnYear01 4.48%
5 years rr_AverageAnnualReturnYear05 (3.67%)
10 years rr_AverageAnnualReturnYear10 (0.31%)
George Putnam Balanced Fund | after taxes on distributions and sale of fund shares | Class A
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Share class rr_AverageAnnualReturnColumnName Class A
Label rr_AverageAnnualReturnLabel after taxes on distributions and sale of fund shares
1 year rr_AverageAnnualReturnYear01 3.36%
5 years rr_AverageAnnualReturnYear05 (2.29%)
10 years rr_AverageAnnualReturnYear10 0.31%
George Putnam Balanced Fund | Russell 1000 Value Index
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Label rr_AverageAnnualReturnLabel Russell 1000 Value Index
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (no deduction for fees, expenses or taxes)
1 year rr_AverageAnnualReturnYear01 15.51%
5 years rr_AverageAnnualReturnYear05 1.28%
10 years rr_AverageAnnualReturnYear10 3.26%
George Putnam Balanced Fund | Barclays Capital U.S. Aggregate Bond Index
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Label rr_AverageAnnualReturnLabel Barclays Capital U.S. Aggregate Bond Index
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (no deduction for fees, expenses or taxes)
1 year rr_AverageAnnualReturnYear01 6.54%
5 years rr_AverageAnnualReturnYear05 5.80%
10 years rr_AverageAnnualReturnYear10 5.84%
George Putnam Balanced Fund | George Putnam Blended Index
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Label rr_AverageAnnualReturnLabel George Putnam Blended Index
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (no deduction for fees, expenses or taxes)
1 year rr_AverageAnnualReturnYear01 12.44%
5 years rr_AverageAnnualReturnYear05 4.09%
10 years rr_AverageAnnualReturnYear10 5.01%
[1] Applies only to certain redemptions of shares bought with no initial sales charge.
[2] This charge is phased out over six years.
[3] This charge is eliminated after one year.