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Warrant Liability - Additional Information (Detail) (USD $) | 1 Months Ended | 12 Months Ended | 6 Months Ended | 1 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Jul. 31, 2014 | Oct. 31, 2013 | Nov. 30, 2008 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Jun. 30, 2012 | Nov. 30, 2009 | Dec. 31, 2011
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Exercise price of warrants | $ 2.17 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 | $ 1.80 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 |  |  |  |  |  |  |
Warrants expired unexercised |  |  | 2014-05 |  |  |  |  |  |
Number of shares issued upon warrants exercise | 11,299,435 us-gaap_StockIssuedDuringPeriodSharesNewIssues | 12,845,500 us-gaap_StockIssuedDuringPeriodSharesNewIssues |  |  |  |  |  |  |
Outstanding Warrants [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Number of shares of common stock in each unit sold to institutional investors | 1 stem_InstitutionalInvestorsUnitsCommonStockSharesIssuedPerUnit / us-gaap_ClassOfWarrantOrRightAxis = us-gaap_WarrantMember | 1 stem_InstitutionalInvestorsUnitsCommonStockSharesIssuedPerUnit / us-gaap_ClassOfWarrantOrRightAxis = us-gaap_WarrantMember | 1 stem_InstitutionalInvestorsUnitsCommonStockSharesIssuedPerUnit / us-gaap_ClassOfWarrantOrRightAxis = us-gaap_WarrantMember |  |  |  |  |  |
Series A Warrants [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Exercise price of warrants |  |  |  | $ 1.40 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember |  |  |  |  |
Proceeds from sale of stock |  |  |  | $ 1,652,000 us-gaap_SaleOfStockConsiderationReceivedOnTransaction / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember | $ 538,000 us-gaap_SaleOfStockConsiderationReceivedOnTransaction / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember | $ 3,078,000 us-gaap_SaleOfStockConsiderationReceivedOnTransaction / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Number of securities callable by each warrant or right warrants | 0.85 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember | 0.5 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |  |  |  |  |
Number of shares of common stock in each unit sold to institutional investors | 1 stem_InstitutionalInvestorsUnitsCommonStockSharesIssuedPerUnit / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember | 1 stem_InstitutionalInvestorsUnitsCommonStockSharesIssuedPerUnit / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |  |  |  |  |
Number of securities callable by warrants |  |  |  | 1,180,015 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |  |  |
Number of shares issued upon warrants exercise |  |  |  |  |  | 2,198,571 stem_NumberOfWarrantExercised / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember | 2,700,000 stem_NumberOfWarrantExercised / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |
November 2008 Financing [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Number of units sold to investors |  |  | 1,379,310 stem_NumberOfWarrantUnitSold / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandEightFinancingMember |  |  |  |  |  |
Price per unit |  |  | 14.50 stem_CapitalUnitsPricePerUnit / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandEightFinancingMember |  |  |  |  |  |
Gross proceeds from units sold to investors |  |  | 20,000,000 us-gaap_CapitalUnitsTotalCostToInvestors / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandEightFinancingMember |  |  |  |  |  |
Proceeds from sale of stock |  |  | 18,637,000 us-gaap_SaleOfStockConsiderationReceivedOnTransaction / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandEightFinancingMember |  |  |  |  |  |
November 2008 Financing [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Number of securities callable by each warrant or right warrants |  |  | 0.75 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandEightFinancingMember |  |  |  |  |  |
Exercise price of warrants |  |  | 23.00 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandEightFinancingMember |  |  |  |  |  |
Number of securities callable by warrants |  |  | 1,034,483 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandEightFinancingMember |  |  |  |  |  |
November 2009 Financing [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Price per unit |  |  |  |  |  |  |  | $ 12.50 stem_CapitalUnitsPricePerUnit / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandNineFinancingMember |
Gross proceeds from units sold to investors |  |  |  |  |  |  |  | 12,500,000 us-gaap_CapitalUnitsTotalCostToInvestors / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandNineFinancingMember |
Exercise price of warrants |  |  |  | $ 15.00 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandNineFinancingMember |  |  |  |  |
Proceeds from sale of stock |  |  |  |  |  |  |  | $ 11,985,000 us-gaap_SaleOfStockConsiderationReceivedOnTransaction / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandNineFinancingMember |
Number of units sold to investors |  |  |  |  |  |  |  | 1,000,000 stem_CapitalUnitsNumberOfUnitsSoldToInvestors / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandNineFinancingMember |
November 2009 Financing [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Number of securities callable by each warrant or right warrants |  |  |  |  |  |  |  | 0.40 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandNineFinancingMember |
Exercise price of warrants |  |  |  |  |  |  |  | $ 15.00 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandNineFinancingMember |
Number of securities callable by warrants |  |  |  |  |  |  |  | 400,000 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandNineFinancingMember |
Number of warrants in each unit sold to institutional investors |  |  |  |  |  |  |  | 1 stem_InstitutionalInvestorsUnitsWarrantsIssuedPerUnit / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_NovemberTwoThousandNineFinancingMember |
December 2011 Financing [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Price per unit |  |  |  |  |  |  |  |  | $ 1.25 stem_CapitalUnitsPricePerUnit / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember
Number of units sold to investors |  |  |  |  |  |  |  |  | 10,000,000 stem_CapitalUnitsNumberOfUnitsSoldToInvestors / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember
Number of Series A warrants in each unit issued in public offering |  |  |  |  |  |  |  |  | 1 stem_PublicOfferedUnitsSeriesWarrantsIssuedPerUnit / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember
December 2011 Financing [Member] | Series A Warrants [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Number of securities callable by warrants |  |  |  |  |  |  |  |  | 8,000,000 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember
Warrant expiration |  |  |  | December 2016 |  |  |  |  |
Number of warrants exercised |  |  |  | 1,180,015 stem_WarrantIssuedForWarrantExercised / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember | 384,534 stem_WarrantIssuedForWarrantExercised / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember | 2,198,571 stem_WarrantIssuedForWarrantExercised / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember |  |  |
Number of shares issued upon warrants exercise |  |  |  |  |  | 2,700,000 stem_NumberOfWarrantExercised / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember |  |  |
December 2011 Financing [Member] | Series B Warrant [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Number of securities callable by warrants |  |  |  |  |  |  |  |  | 8,000,000 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesBWarrantMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember
Term of warrant |  |  |  |  |  |  |  |  | 90 days
Warrant expiration |  |  |  | 2012-May-02 |  |  |  |  |
Number of warrants exercised |  |  |  |  |  | 2,700,000 stem_WarrantIssuedForWarrantExercised / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesBWarrantMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember |  |  |
Number of warrants expired |  |  |  | 5,300,000 stem_ClassOfWarrantOrRightNumberOfWarrantsOrRightsExpired / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesBWarrantMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember |  |  |  |  |
December 2011 Financing [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Number of securities callable by each warrant or right warrants |  |  |  | 1 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember |  |  |  |  |
Number of shares issued upon warrants exercise |  |  |  |  | 384,534 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember | 2,700,000 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember |  |  |
Number of shares issued upon warrants exercise |  |  |  | 1,180,015 stem_NumberOfWarrantExercised / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember | 384,534 stem_NumberOfWarrantExercised / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember | 2,198,571 stem_NumberOfWarrantExercised / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember |  |  |
December 2011 Financing [Member] | Common Stock [Member] | Series A Warrants [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Exercise price of warrants |  |  |  |  |  |  |  |  | $ 1.40 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember
December 2011 Financing [Member] | Capital Units [Member] | Series A Warrants [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Number of securities callable by each warrant or right warrants |  |  |  |  |  |  |  |  | 1 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CapitalUnitsMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember
December 2011 Financing [Member] | Capital Units [Member] | Series B Warrant [Member] |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Number of securities callable by each warrant or right warrants |  |  |  |  |  |  |  |  | 1 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesBWarrantMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CapitalUnitsMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember

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