Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity (Details 4)

v2.4.1.9
Stockholders' Equity (Details 4) (USD $)
12 Months Ended 1 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Aug. 31, 2010
May 31, 2014
Jun. 30, 2000
Shares            
Nonvested, balance at the beginning of the period (in shares) 2,100,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber 1,500,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber        
Nonvested, balance at the end of the period (in shares) 1,900,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber 2,100,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber 1,500,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber      
Additional disclosure            
Stock-based compensation expense $ 2,236,000us-gaap_AllocatedShareBasedCompensationExpense $ 2,147,000us-gaap_AllocatedShareBasedCompensationExpense $ 1,601,000us-gaap_AllocatedShareBasedCompensationExpense      
Purchase Plan            
Additional disclosure            
Increase in common stock available under the plan       500,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ us-gaap_PlanNameAxis
= us-gaap_EmployeeStockMember
   
Expiration term from approval of grant       10 years    
Number of shares of common stock reserved for issuance       1,400,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= us-gaap_EmployeeStockMember
  900,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= us-gaap_EmployeeStockMember
Maximum amount that can be contributed by the employee 25,000cpst_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumContributionByEmployeeAmount
/ us-gaap_PlanNameAxis
= us-gaap_EmployeeStockMember
         
Maximum percentage of regular compensation that can be contributed by the employee 15.00%cpst_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumContributionByEmployeePercent
/ us-gaap_PlanNameAxis
= us-gaap_EmployeeStockMember
         
Percentage of the fair market value of common stock on the last day of the purchase right period 95.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent
/ us-gaap_PlanNameAxis
= us-gaap_EmployeeStockMember
         
Options granted (in shares) 20,619us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= us-gaap_EmployeeStockMember
12,302us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= us-gaap_EmployeeStockMember
22,478us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= us-gaap_EmployeeStockMember
     
Number of shares available for future grant 409,569us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= us-gaap_EmployeeStockMember
         
Restricted stock units            
Shares            
Nonvested, balance at the end of the period (in shares) 93,750us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
         
Additional disclosure            
Vesting period 4 years          
Stock-based compensation expense 1,048,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
914,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
558,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
     
Aggregate fair value of restricted stock units vested and issued 1,206,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
806,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
560,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
     
Weighted average grant date fair value of options granted during the period (in dollars per share) $ 1.33us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
$ 1.09us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
$ 1.00us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
     
Unrecognized compensation cost 1,400,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
         
Weighted average period for recognizing compensation cost 2 years 1 month 6 days          
Restricted stock units | Awards vesting over four years with one-fourth units vesting one year after the issuance date            
Additional disclosure            
Vesting period 1 year          
Awards vesting percentage 25.00%cpst_VestingRightsPercentage
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_AwardsVestingOverFourYearsWithOneFourthUnitsVestingOneYearAfterIssuanceDateMember
         
Restricted stock units | Performance Restricted Stock Units            
Shares            
Nonvested, balance at the beginning of the period (in shares) 2,061,224us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
Granted (in shares) 974,236us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
Vested and issued (in shares) (828,136)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
PRSU adjustments (200,000)cpst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPerformanceRestrictedStockUnitAdjustmentsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
Forfeited (in shares) (138,750)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
Nonvested, balance at the end of the period (in shares) 1,868,574us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
Awards expected to vest (in shares) 1,760,706cpst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectedToVestOutstandingNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
Weighted Average Grant-Date Fair Value            
Nonvested restricted stock units outstanding at the beginning of the period (in dollars per share) $ 1.11us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
Granted (in dollars per share) $ 1.37us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
Vested and issued (in dollars per share) $ 1.13us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
PRSU adjustments (in dollars per share) $ 1.56cpst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPerformanceRestictedStockUnitAdjustmentsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
Forfeited (in dollars per share) $ 1.14us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
Nonvested restricted stock units outstanding at the end of the period (in dollars per share) $ 1.19us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
Awards expected to vest (in dollars per share) $ 1.19cpst_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectedToVestWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= cpst_PerformanceBasedRestrictedStockUnitsMember
         
Non-employee director            
Weighted Average Grant-Date Fair Value            
Granted (in dollars per share) $ 0.99us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
$ 1.26us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
$ 0.98us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
     
Additional disclosure            
Stock-based compensation expense 117,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
116,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
101,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
     
Deferred stock awards granted 119,277us-gaap_StockIssuedDuringPeriodSharesIssuedForServices
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
91,603us-gaap_StockIssuedDuringPeriodSharesIssuedForServices
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
103,574us-gaap_StockIssuedDuringPeriodSharesIssuedForServices
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
     
Non-employee director | Restricted stock units            
Additional disclosure            
Vesting period 1 year          
Chief Executive Officer | PRSU Program            
Shares            
Granted (in shares) 200,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= cpst_PerformanceRestrictedStockUnitProgramMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefExecutiveOfficerMember
         
Additional disclosure            
Stock-based compensation expense $ 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= cpst_PerformanceRestrictedStockUnitProgramMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefExecutiveOfficerMember
         
Weighted average grant date fair value of options granted during the period (in dollars per share) $ 1.56us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= cpst_PerformanceRestrictedStockUnitProgramMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefExecutiveOfficerMember
         
Vesting right percentage of awards that will vest after end of applicable performance measurement period         50.00%cpst_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentageThatWillVestAfterEndOfPerformanceMeasurementPeriod
/ us-gaap_AwardTypeAxis
= cpst_PerformanceRestrictedStockUnitProgramMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefExecutiveOfficerMember
 
Vesting right percentage of awards that will vest one year after end of performance measurement period         50.00%cpst_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentageThatWillVestOneYearAfterEndOfPerformanceMeasurementPeriod
/ us-gaap_AwardTypeAxis
= cpst_PerformanceRestrictedStockUnitProgramMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_ChiefExecutiveOfficerMember