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Warrant Liability - Assumptions Used for Monte Carlo Simulation Model (Detail) (Series A Warrants [Member])
3 Months Ended
Mar. 31, 2015
Series A Warrants [Member]
 
Class of Warrant or Right [Line Items]  
Risk-free interest rate per year 0.45%us-gaap_FairValueAssumptionsRiskFreeInterestRate
/ us-gaap_SubsidiarySaleOfStockAxis
= stem_SeriesWarrantMember
Expected volatility per year 57.80%us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate
/ us-gaap_SubsidiarySaleOfStockAxis
= stem_SeriesWarrantMember
Expected dividend yield 0.00%us-gaap_FairValueAssumptionsExpectedDividendRate
/ us-gaap_SubsidiarySaleOfStockAxis
= stem_SeriesWarrantMember
Expected life (years) 1 year 8 months 12 days