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Common Stock - Additional Information (Detail) (USD $) | 1 Months Ended | 12 Months Ended | 1 Months Ended | 6 Months Ended | 1 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Jul. 31, 2014 | Oct. 31, 2013 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Jun. 30, 2013 | Nov. 30, 2008 | Jun. 30, 2012 | Dec. 31, 2012 | Dec. 31, 2011
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock issued in public offering | 11,299,435 us-gaap_StockIssuedDuringPeriodSharesNewIssues | 12,845,500 us-gaap_StockIssuedDuringPeriodSharesNewIssues |  |  |  |  |  |  |  |
Sale of common stock and warrant, price per share | $ 1.77 stem_StockIssuedDuringPeriodNewIssuesSellingPricePerShare | $ 1.45 stem_StockIssuedDuringPeriodNewIssuesSellingPricePerShare |  | $ 1.91 stem_StockIssuedDuringPeriodNewIssuesSellingPricePerShare | $ 2.12 stem_StockIssuedDuringPeriodNewIssuesSellingPricePerShare |  |  |  |  |
Proceeds from issuance of common stock and warrants | $ 20,000,000 stem_ProceedsFromIssuanceOfCommonStockAndWarrants | $ 17,300,000 stem_ProceedsFromIssuanceOfCommonStockAndWarrants |  |  |  |  |  |  |  |
Warrant exercise price | $ 2.17 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 | $ 1.80 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 |  |  |  |  |  |  |  |
Warrant expiration period | 13 months | 5 years |  |  |  |  |  |  |  |
Gross proceeds |  |  | 1,974,931 us-gaap_ProceedsFromWarrantExercises | 530,097 us-gaap_ProceedsFromWarrantExercises | 6,256,438 us-gaap_ProceedsFromWarrantExercises |  |  |  |  |
Percentage of compensation paid to sales agent |  |  |  | 3.00%stem_PercentageOfGrossProceedsPaidToAgent | 3.00%stem_PercentageOfGrossProceedsPaidToAgent |  |  |  |  |
Gross proceeds from common stock |  |  | 18,949,647 us-gaap_ProceedsFromIssuanceOfCommonStock | 23,491,597 us-gaap_ProceedsFromIssuanceOfCommonStock | 19,747,550 us-gaap_ProceedsFromIssuanceOfCommonStock |  |  |  |  |
Common stock, par value |  | $ 0.01 us-gaap_CommonStockParOrStatedValuePerShare | $ 0.01 us-gaap_CommonStockParOrStatedValuePerShare | $ 0.01 us-gaap_CommonStockParOrStatedValuePerShare |  |  |  |  |  |
Warrants termination agreement |  |  | 2013-10 |  |  |  |  |  |  |
Common stock, sold |  |  |  | 1,733,771 us-gaap_StockIssuedDuringPeriodSharesIssuedForCash | 9,647,471 us-gaap_StockIssuedDuringPeriodSharesIssuedForCash |  |  |  |  |
Institutional Investors [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Shares available to sale |  |  |  |  |  | 30,000,000 stem_SaleOfStockValueOfSharesAvailableForTransaction / us-gaap_RelatedPartyTransactionAxis = stem_InstitutionalInvestorsMember |  |  |  |
Gross proceeds from common stock |  |  |  |  |  | 3,000,000 us-gaap_ProceedsFromIssuanceOfCommonStock / us-gaap_RelatedPartyTransactionAxis = stem_InstitutionalInvestorsMember |  |  |  |
Exercise period of rights |  |  |  |  |  | 3 years |  |  |  |
Additional amounts of common stock to sell |  |  |  |  |  | 27,000,000 stem_RightToSellCommonStockAdditionalAmounts / us-gaap_RelatedPartyTransactionAxis = stem_InstitutionalInvestorsMember |  |  |  |
Outstanding Warrants [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares of common stock or warrant 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] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Warrant exercise price |  |  | $ 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 |  |  |  |  |
Series A Warrants [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares exercise |  |  | 1,180,015 stem_ClassOfWarrantOrRightExerciseOfWarrantsOrRights / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesAWarrantsMember |  |  |  |  |  |  |
Gross proceeds |  |  | 1,652,000 us-gaap_ProceedsFromWarrantExercises / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesAWarrantsMember |  |  |  |  |  |  |
Series B Warrant [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Gross proceeds |  |  |  |  |  |  |  | 3,375,000 us-gaap_ProceedsFromWarrantExercises / us-gaap_StatementClassOfStockAxis = stem_SeriesBWarrantMember |  |
Number of warrants exercised |  |  |  |  |  |  |  | 2,700,000 stem_WarrantIssuedForWarrantExercised / us-gaap_StatementClassOfStockAxis = stem_SeriesBWarrantMember |  |
Number of warrants expired |  |  |  |  | 5,300,000 stem_ClassOfWarrantOrRightNumberOfWarrantsOrRightsExpired / us-gaap_StatementClassOfStockAxis = stem_SeriesBWarrantMember |  |  |  |  |
Warrant expiration date |  |  |  |  | May 02, 2012 |  |  |  |  |
Series A Warrants [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Gross proceeds |  |  |  |  | 3,078,000 us-gaap_ProceedsFromWarrantExercises / us-gaap_StatementClassOfStockAxis = stem_SeriesWarrantMember |  |  |  |  |
Number of warrants exercised |  |  | 1,180,015 stem_ClassOfWarrantOrRightNumberOfWarrantsOrRightsExercised / us-gaap_StatementClassOfStockAxis = stem_SeriesWarrantMember |  |  |  |  |  |  |
Number of warrants exercised |  |  |  |  | 2,198,571 stem_WarrantIssuedForWarrantExercised / us-gaap_StatementClassOfStockAxis = stem_SeriesWarrantMember |  |  |  |  |
Number of warrants issued |  |  |  |  |  |  |  | 2,700,000 stem_NumberOfSeriesWarrantsIssued / us-gaap_StatementClassOfStockAxis = stem_SeriesWarrantMember |  |
December 2011 Financing [Member] | Series A Warrants [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Numbers of share issued |  |  |  |  |  |  |  |  |  | 8,000,000 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember
Number of warrants exercised |  |  |  | 384,534 stem_ClassOfWarrantOrRightNumberOfWarrantsOrRightsExercised / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember |  |  |  |  |  |
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 A Warrants [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of securities callable by each warrant or right warrants |  |  | 1 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesAWarrantsMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember |  |  |  |  |  |  |
Numbers of share issued |  |  |  |  |  |  |  |  |  | 8,000,000 us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesAWarrantsMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember
2012 Amended Sales Agreement [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Percentage of compensation paid to sales agent |  |  | 2.00%stem_PercentageOfGrossProceedsPaidToAgent / us-gaap_SubsidiarySaleOfStockAxis = stem_TwoThousandTwelveAmendedSalesAgreementMember |  |  |  |  |  |  |
Shares available to sale |  |  |  |  |  |  |  |  | 30,000,000 stem_SaleOfStockValueOfSharesAvailableForTransaction / us-gaap_SubsidiarySaleOfStockAxis = stem_TwoThousandTwelveAmendedSalesAgreementMember |
Gross proceeds from common stock |  |  | $ 285,000 us-gaap_ProceedsFromIssuanceOfCommonStock / us-gaap_SubsidiarySaleOfStockAxis = stem_TwoThousandTwelveAmendedSalesAgreementMember |  |  |  |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares of common stock or warrant 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 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 |  |  |  |  |  |  |  |
Numbers of share issued |  |  | 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 |  |
Common Stock [Member] | Institutional Investors [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock issued in public offering |  |  |  |  |  | 329,131 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_RelatedPartyTransactionAxis = stem_InstitutionalInvestorsMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |  |
Common stock, sold |  |  |  |  |  | 1,645,639 us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction / us-gaap_RelatedPartyTransactionAxis = stem_InstitutionalInvestorsMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |  |
Sale of stock, price per share |  |  |  |  |  | $ 1.823 us-gaap_SaleOfStockPricePerShare / us-gaap_RelatedPartyTransactionAxis = stem_InstitutionalInvestorsMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |  |
Common Stock [Member] | December 2011 Financing [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock issued in public offering |  |  |  | 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 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 |  |  | 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 |  |  |  |  |
Common Stock [Member] | December 2011 Financing [Member] | Series A Warrants [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Warrant exercise price |  |  |  |  |  |  |  |  |  | 1.40 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesWarrantMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember
Common Stock [Member] | December 2011 Financing [Member] | Series A Warrants [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Warrant exercise price |  |  |  |  |  |  |  |  |  | 1.40 us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 / us-gaap_ClassOfWarrantOrRightAxis = stem_SeriesAWarrantsMember / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_DecemberTwoThousandElevenFinancingMember
Common Stock [Member] | 2012 Amended Sales Agreement [Member] |  |  |  |  |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock, sold |  |  | 193,271 us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_TwoThousandTwelveAmendedSalesAgreementMember |  |  |  |  |  |  |
Sale of stock, price per share |  |  | $ 1.47 us-gaap_SaleOfStockPricePerShare / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsidiarySaleOfStockAxis = stem_TwoThousandTwelveAmendedSalesAgreementMember |  |  |  |  |  |  |

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