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Stockholders' Equity - Additional Information (Detail) (USD $) | 0 Months Ended | 3 Months Ended | 12 Months Ended |  |
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Apr. 03, 2013 | Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2012 | Sep. 30, 2012 | Jun. 30, 2012 | Mar. 31, 2012 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Apr. 30, 2014 | Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares authorized |  | 500,000 us-gaap_PreferredStockSharesAuthorized |  |  |  | 500,000 us-gaap_PreferredStockSharesAuthorized |  |  |  |  |  |  |  | 500,000 us-gaap_PreferredStockSharesAuthorized | 500,000 us-gaap_PreferredStockSharesAuthorized |  |  |
Preferred stock, par value |  | $ 0.01 us-gaap_PreferredStockParOrStatedValuePerShare |  |  |  | $ 0.01 us-gaap_PreferredStockParOrStatedValuePerShare |  |  |  |  |  |  |  | $ 0.01 us-gaap_PreferredStockParOrStatedValuePerShare | $ 0.01 us-gaap_PreferredStockParOrStatedValuePerShare |  |  |
Authorized to purchase of common stock under the stock repurchase program |  | $ 410,000,000 us-gaap_StockRepurchaseProgramAuthorizedAmount1 |  |  |  |  |  |  |  |  |  |  |  | $ 410,000,000 us-gaap_StockRepurchaseProgramAuthorizedAmount1 |  |  | $ 25,000,000 us-gaap_StockRepurchaseProgramAuthorizedAmount1 |
Cumulative repurchase of common stock |  | 14,400,000 forr_CumulativeRepurchaseOfCommonStock |  |  |  |  |  |  |  |  |  |  |  | 14,400,000 forr_CumulativeRepurchaseOfCommonStock |  |  |  |
Aggregate cost of repurchase of common stock |  |  |  |  |  |  |  |  |  |  |  |  |  | 402,200,000 forr_CumulativeCommonStockPurchasedProgramLifeToDateValue |  |  |  |
Tender offer repurchase maximum | 130,000,000 forr_StockRepurchaseProgramTenderOfferRepurchaseMaximumAmount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tender offer increment in per share value | $ 0.25 forr_StockRepurchaseProgramTenderOfferAuthorizedIncrementalPricePerShare |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tender Offer purchase of common stock | 2,054,732 forr_StockRepurchaseProgramTenderOfferNumberOfSharesPurchased |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tender offer purchase price of common stock per share | $ 36.00 forr_StockRepurchaseProgramTenderOfferPurchasePricePerShare |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tender offer shares aggregate purchase price | 74,000,000 forr_StockRepurchaseProgramTenderOfferSharesPurchasedAggregateValue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expenses related to tender offer | 1,100,000 forr_StockRepurchaseProgramTenderOfferExpenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tender offer expired date | May 01, 2013 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Treasury stock, retired |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 11,700,000 us-gaap_TreasuryStockSharesRetired |  |  |
Carrying value of retired stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 303,000,000 us-gaap_TreasuryStockRetiredCostMethodAmount |  |  |
Dividend declared and paid per share |  | $ 0.16 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.16 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.16 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.16 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.15 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.15 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.15 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.15 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.14 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.14 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.14 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.14 us-gaap_CommonStockDividendsPerShareCashPaid |  |  |  |  |
Dividend declared per share |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.64 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.60 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.56 us-gaap_CommonStockDividendsPerShareDeclared |  |
Aggregate dividend declared for the year |  |  |  |  |  |  |  |  |  |  |  |  |  | 12,000,000 us-gaap_Dividends | 12,400,000 us-gaap_Dividends | 12,600,000 us-gaap_Dividends |  |
Option Outstanding and vested |  | 1,954,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber |  |  |  | 1,734,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber |  |  |  |  |  |  |  | 1,954,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber | 1,734,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber |  |  |
Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tender offer authorized price per share | $ 32.00 forr_StockRepurchaseProgramTenderOfferAuthorizedPricePerShare / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tender offer authorized price per share | $ 36.00 forr_StockRepurchaseProgramTenderOfferAuthorizedPricePerShare / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future awards granted or issued under plans |  | 12,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |  |  |  |  |  |  |  |  | 12,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
Number of installments upon which share based awards vest |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 forr_NumberOfVestInstallmentsShareBasedAwards / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
Restricted Stock Units (RSUs) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average grant date fair value for RSUs granted |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 36.67 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember | $ 34.58 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember | $ 33.88 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  |
Number of shares received per restricted stock unit on lapse of restrictions and vesting condition met |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 forr_NumberOfSharesVestedPerRestrictedStockUnitsOnRestrictionLapseAndVestingConditionMet / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  |  |  |
Value of RSUs vested and converted to common stock |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,500,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember | 2,400,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember | 1,600,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember |  |
Restricted Stock Units (RSUs) [Member] | Equity Plan [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Options vested period |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 years |  |  |  |
Restricted Stock Units (RSUs) [Member] | Equity Plan [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Options vested period |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 years |  |  |  |
Stock Options [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intrinsic value of options exercised |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,300,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | 6,100,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | 3,500,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember |  |
2006 Equity Plan [Member] | Equity Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future awards granted or issued under plans |  | 1,300,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = forr_TwoThousandSixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |  |  |  |  |  |  |  |  | 1,300,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = forr_TwoThousandSixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
Shares authorized |  |  |  |  |  |  |  |  |  | 4,350,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = forr_TwoThousandSixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |  |  | 4,350,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = forr_TwoThousandSixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |
Options vested period |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 years |  |  |  |
Option expiration period |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 years |  |  |  |
1996 Equity Plan [Member] | Equity Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future awards granted or issued under plans |  | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |  |  |  |  |  |  |  |  | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
Shares authorized |  | 13,500,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |  |  |  |  |  |  |  |  | 13,500,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
Shares returned |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,500,000 forr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfShareReturnedFromPreviousPlan / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |
Option expiration period |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 years |  |  |  |
Percentage of voting rights that trigger ISO fmv grant conditions |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.00%forr_ShareBasedCompensationArrangementByShareBasedPaymentAwardVotingRights / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
Exercise price rate of fair value |  |  |  |  |  |  |  |  |  |  |  |  |  | 110.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
Option Outstanding and vested |  | 24,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |  |  |  |  |  |  |  |  | 24,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
1996 Equity Plan [Member] | Equity Plan [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Options vested period |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 years |  |  |  |
1996 Equity Plan [Member] | Equity Plan [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Options vested period |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 years |  |  |  |
2006 Director Plan [Member] | Equity Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future awards granted or issued under plans |  | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = forr_TwoThousandSixDirectorPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |  |  |  |  |  |  |  |  | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = forr_TwoThousandSixDirectorPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
Shares authorized |  | 450,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = forr_TwoThousandSixDirectorPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |  |  |  |  |  |  |  |  | 450,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = forr_TwoThousandSixDirectorPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
Shares returned |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 80,000 forr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfShareReturnedFromPreviousPlan / us-gaap_PlanNameAxis = forr_TwoThousandSixDirectorPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |
Option Outstanding and vested |  | 200,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_PlanNameAxis = forr_TwoThousandSixDirectorPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |  |  |  |  |  |  |  |  | 200,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_PlanNameAxis = forr_TwoThousandSixDirectorPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
Number of shares of common stock options entitlement of non- employee directors |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6,000 forr_DeferredCompensationArrangementWithIndividualOptionGrantDuringPeriod / us-gaap_PlanNameAxis = forr_TwoThousandSixDirectorPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember
Employee Stock Purchase Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future awards granted or issued under plans |  | 300,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = forr_EmployeeStockPurchasePlanMember |  |  |  |  |  |  |  |  |  |  |  | 300,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = forr_EmployeeStockPurchasePlanMember |  |  |  |
Shares authorized |  | 1,500,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = forr_EmployeeStockPurchasePlanMember |  |  |  |  |  |  |  |  |  |  |  | 1,500,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = forr_EmployeeStockPurchasePlanMember |  |  |  |
Exercise price rate of fair value |  |  |  |  |  |  |  |  |  |  |  |  |  | 85.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent / us-gaap_PlanNameAxis = forr_EmployeeStockPurchasePlanMember |  |  |  |
Hours of work per week |  |  |  |  |  |  |  |  |  |  |  |  |  | 20 forr_ShareBasedCompensationArrangementByShareBasedPaymentAwardRequisiteServiceHoursPerWeek / us-gaap_PlanNameAxis = forr_EmployeeStockPurchasePlanMember |  |  |  |
Duration of purchase periods under employee stock purchase plan |  |  |  |  |  |  |  |  |  |  |  |  |  | 6 months |  |  |  |
Holding period of stocks acquired under employee stock purchase plan |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 year |  |  |  |
Value used to derive maximum number of shares per participant for employee stock purchase |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 12,500 forr_ValueToDeriveMaximumNumberOfSharesForPurchase / us-gaap_PlanNameAxis = forr_EmployeeStockPurchasePlanMember |  |  |  |
Employee maximum elected percentage reduction of compensation to purchase shares |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.00%forr_PercentOfDeductionInCompensationForSharePurchaseUnderStockPurchasePlan / us-gaap_PlanNameAxis = forr_EmployeeStockPurchasePlanMember |  |  |  |
1996 Director [Member] | Equity Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future awards granted or issued under plans |  | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityDirectorPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |  |  |  |  |  |  |  |  | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityDirectorPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
Option Outstanding and vested |  | 13,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityDirectorPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |  |  |  |  |  |  |  |  | 13,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_PlanNameAxis = forr_OneThousandNineHundredNinetySixEquityDirectorPlanMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |
Prior to 2011 [Member] | Equity Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future awards granted or issued under plans |  | 12,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = forr_PriorMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |  |  |  |  |  |  |  |  | 12,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = forr_PriorMember / us-gaap_TradingActivityByTypeAxis = us-gaap_EquityMember |  |  |  |

X
- Definition Value of shares of common stock repurchased under the stock repurchase program over the life of the plan to date. + References No definition available. + Details
Name: | forr_CumulativeCommonStockPurchasedProgramLifeToDateValue
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