Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Details)

v2.4.1.9
Summary of Significant Accounting Policies (Details) (USD $)
12 Months Ended 9 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Dec. 31, 2014
Sep. 30, 2013
Inventories          
Increase in inventory charges $ 1,000,000us-gaap_IncreaseDecreaseInDeferredCharges        
Long-Lived Assets          
Impairment 0us-gaap_AssetImpairmentCharges        
Revenue          
Term for advance payment from shipment of sales 90 days        
Research and Development ("R&D")          
Total offsets to R&D expenses 500,000cpst_ResearchAndDevelopmentOffsetToExpenses 1,400,000cpst_ResearchAndDevelopmentOffsetToExpenses 1,700,000cpst_ResearchAndDevelopmentOffsetToExpenses    
Risk Concentrations          
Aggregate balances that exceed insurance coverage 32,000,000us-gaap_CashUninsuredAmount        
Bad debt expense 10,138,000us-gaap_ProvisionForDoubtfulAccounts 242,000us-gaap_ProvisionForDoubtfulAccounts 276,000us-gaap_ProvisionForDoubtfulAccounts    
Net Loss Per Common Share          
Options outstanding (in shares) 13,200,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber 12,900,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber 11,800,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber    
Outstanding restricted stock units (in shares) 1,900,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber 2,100,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber 1,500,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber    
Number of warrants excluded from diluted net loss per common share computations 0us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount 0us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount 26,500,000us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount    
Revenue | Customer concentrations | E-Finity          
Risk Concentrations          
Concentration percentage   19.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_EFinityDistributedGenerationMember
     
Revenue | Customer concentrations | Horizon          
Risk Concentrations          
Concentration percentage 17.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_HorizonPowerSystemsMember
12.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_HorizonPowerSystemsMember
27.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_HorizonPowerSystemsMember
   
Revenue | Customer concentrations | BPC          
Risk Concentrations          
Concentration percentage 11.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_BankingProductionCentreMember
17.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_BankingProductionCentreMember
11.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_BankingProductionCentreMember
   
Accounts receivable allowance 7,100,000us-gaap_AllowanceForDoubtfulAccountsReceivable
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_BankingProductionCentreMember
       
Net accounts receivable | Credit concentration | E-Finity          
Risk Concentrations          
Concentration percentage   16.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CreditConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_EFinityDistributedGenerationMember
     
Net accounts receivable | Credit concentration | BPC          
Risk Concentrations          
Concentration percentage   26.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CreditConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_BankingProductionCentreMember
  17.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CreditConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_BankingProductionCentreMember
 
Accounts receivable allowance         $ 2,600,000us-gaap_AllowanceForDoubtfulAccountsReceivable
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CreditConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_BankingProductionCentreMember
Net accounts receivable | Credit concentration | EMI          
Risk Concentrations          
Concentration percentage   18.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CreditConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= cpst_ElectroMecaniqueIndustriesMember
     
Minimum          
Depreciation and Amortization          
Estimated Useful Life 2 years        
Maximum          
Depreciation and Amortization          
Estimated Useful Life 10 years        
Warranty          
Warranty period 18 months