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Stock-Based Compensation - Summary of Changes in Unvested Options (Parenthetical) (Detail) | 3 Months Ended
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Mar. 31, 2016 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Number of options granted | 10,000
Unvested stock options [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Number of options granted | 10,000

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Gross number of share options (or share units) granted during the period. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_AwardTypeAxis=stem_UnvestedStockOptionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |