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Real Estate Assets - Additional Information (Details) - ft² | 1 Months Ended | 6 Months Ended
--- | --- | ---
Feb. 29, 2020 | Jun. 30, 2020
McCordsville, IN |  |
Real Estate Properties [Line Items] |  |
Gross square feet of traditional drive-up storage units and all-climate-controlled units |  | 13,713
Number of leasable unit |  | 7,300
Millbrook, NY |  |
Real Estate Properties [Line Items] |  |
Gross square feet of traditional drive-up storage units and all-climate-controlled units | 11,800 |

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- Definition Leasable square feet. + References No definition available. + Details
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Namespace Prefix: | self_
Data Type: | num:areaItemType
Balance Type: | na
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- Definition Number of leasable units. + References No definition available. + Details
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Namespace Prefix: | self_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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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
Name: | us-gaap_RealEstatePropertiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_StatementGeographicalAxis=self_MillbrookNYMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |