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v3.21.1

Fair Value Measurements - Non-recurring Fair Value Measurements for Impairment (Details) | 3 Months Ended
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Mar. 31, 2021 $ / ft² yr realEstateProperty
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |
Number of properties impaired | realEstateProperty | 2
2200 Channahon Road | Expected selling price per square foot |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |
Expected selling price per square foot | $ / ft² | 8.30
2200 Channahon Road | Estimated hold period |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |
Expected selling price per square foot | yr | 1
Houston Westway I | Expected selling price per square foot |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |
Expected selling price per square foot | $ / ft² | 72.90
Houston Westway I | Estimated hold period |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |
Expected selling price per square foot | yr | 1

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- Definition Number of Impaired Properties + References No definition available. + Details
Name: | gcnl_NumberOfImpairedProperties
Namespace Prefix: | gcnl_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Real Estate Property, Measurement Input + References No definition available. + Details
Name: | gcnl_RealEstatePropertyMeasurementInput
Namespace Prefix: | gcnl_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

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

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- Details
Name: | us-gaap_MeasurementInputTypeAxis=gcnl_ExpectedSellingPricePerSquareFootMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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