Debt Instrument, Number of Instruments

No definition available.

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- Definition

Line of Credit Facility, Covenant, Aggregate Maximum, Percentage of Total Asset Value

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantAggregateMaximumPercentageofTotalAssetValue
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Aggregate Maximum Unhedged Variable Rate Debt, Percent of Asset Value

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantAggregateMaximumUnhedgedVariableRateDebtPercentofAssetValue
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Investments in Mortgage Notes Receivable, Maximum Percentage of Total Asset Value

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantInvestmentsinMortgageNotesReceivableMaximumPercentageofTotalAssetValue
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Investments in Unconsolidated Affiliates, Maximum Percentage of Total Asset Value

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantInvestmentsinUnconsolidatedAffiliatesMaximumPercentageofTotalAssetValue
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Leases Assets Under Renovation, Maximum Percentage of Total Asset Value

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantLeasesAssetsUnderRenovationMaximumPercentageofTotalAssetValue
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Maximum Consolidated Leverage Ratio

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantMaximumConsolidatedLeverageRatio
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Maximum Consolidated Leverage Ratio After Material Acquisition

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantMaximumConsolidatedLeverageRatioAfterMaterialAcquisition
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Maximum Consolidated Leverage Ratio, Number of Quarters of Higher Maximum

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantMaximumConsolidatedLeverageRatioNumberofQuartersofHigherMaximum
Namespace Prefix:	gcnl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of Credit Facility, Covenant, Maximum Payout Ratio

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantMaximumPayoutRatio
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Maximum Total Secured Debt Ratio

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantMaximumTotalSecuredDebtRatio
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Maximum Total Secured Debt Ratio, Increase

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantMaximumTotalSecuredDebtRatioIncrease
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Maximum Total Secured Debt Ratio, Periods of Increased Percentage

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantMaximumTotalSecuredDebtRatioPeriodsofIncreasedPercentage
Namespace Prefix:	gcnl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Maximum Total Secured Recourse Debt Ratio

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantMaximumTotalSecuredRecourseDebtRatio
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Minimum Consolidated Fixed Charge Coverage Ratio

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantMinimumConsolidatedFixedChargeCoverageRatio
Namespace Prefix:	gcnl_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Minimum Unsecured Interest Coverage Ratio

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantMinimumUnsecuredInterestCoverageRatio
Namespace Prefix:	gcnl_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Pre-leased Assets Under Development, Maximum Percentage of Total Asset Value

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantPreleasedAssetsUnderDevelopmentMaximumPercentageofTotalAssetValue
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Tangible Net Worth

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantTangibleNetWorth
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Tangible Net Worth, Additional Percentage of Net Future Equity issuances

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantTangibleNetWorthAdditionalPercentageofNetFutureEquityissuances
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Tangible Net Worth, Reducing Percentage for Redemption Payments

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantTangibleNetWorthReducingPercentageforRedemptionPayments
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Tangible Net Worth, Value

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantTangibleNetWorthValue
Namespace Prefix:	gcnl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line of Credit Facility, Covenant, Unimproved Land, Maximum Percentage of Total Asset Value

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditFacilityCovenantUnimprovedLandMaximumPercentageofTotalAssetValue
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit facility, Covenant, Maximum Pool Value Contributed by Pool Properties Subject to Ground Leases

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditfacilityCovenantMaximumPoolValueContributedbyPoolPropertiesSubjecttoGroundLeases
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit facility, Covenant, Maximum Pool Value Contributed by Poop Properties Under Development or Assets Under Renovation

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditfacilityCovenantMaximumPoolValueContributedbyPoopPropertiesUnderDevelopmentorAssetsUnderRenovation
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit facility, Covenant, Maximum Pool Value Contributed by Single Property or Tenant

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditfacilityCovenantMaximumPoolValueContributedbySinglePropertyorTenant
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit facility, Covenant, Maximum Unsecured Leverage Ratio

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditfacilityCovenantMaximumUnsecuredLeverageRatio
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit facility, Covenant, Minimum Aggregate Leasing Percentage

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditfacilityCovenantMinimumAggregateLeasingPercentage
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit facility, Covenant, Minimum Pool Properties

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditfacilityCovenantMinimumPoolProperties
Namespace Prefix:	gcnl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit facility, Covenant, Minimum Unsecured Coverage Ratio

+ References

No definition available.

+ Details

Name:	gcnl_LineofCreditfacilityCovenantMinimumUnsecuredCoverageRatio
Namespace Prefix:	gcnl_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LoansPayableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gcnl_KeybankLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_MortgagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gcnl_PBVLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	gcnl_AssetAcquisitionAxis=gcnl_PepsiBottlingVenturesMember
Namespace Prefix:
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Period Type:

Debt - Narrative (Details) $ in Thousands	9 Months Ended
Debt - Narrative (Details) $ in Thousands	Sep. 30, 2020 USD ($) quarter property	Feb. 05, 2020 USD ($)	Dec. 31, 2019 USD ($)	Apr. 30, 2019 loan
Debt Instrument [Line Items]
Number of term loans \| loan				3
Debt	$ 2,174,352		$ 1,969,104
Term Loans \| Keybank Loans
Debt Instrument [Line Items]
Compliance requirement - maximum consolidated leverage ratio (percent)	60.00%
Compliance requirement - maximum consolidated leverage ratio after material acquisition (percent)	65.00%
Compliance requirement - consecutive quarters after material acquisition subject to higher consolidated leverage ratio \| quarter	4
Compliance requirement - minimum consolidated tangible net worth (percent)	75.00%
Compliance requirement - minimum consolidated tangible net worth	$ 2,000,000
Compliance requirement - additional net future equity issuances (percent)	75.00%
Compliance requirement - reduction for amount of payments used to redeem stock (percent)	75.00%
Compliance requirement - minimum consolidated fixed charge coverage ratio	1.50
Compliance requirement - maximum total secured debt ratio (percent)	40.00%
Compliance requirement - increase in maximum total secured coverage ratio after material acquisition (percent)	5.00%
Compliance requirement - number of quarters subject to higher maximum total secured coverage ratio after material acquisition \| quarter	4
Compliance requirement - minimum unsecured interest coverage ratio	2.00
Compliance requirement - maximum total secured recourse debt ratio (percent)	10.00%
Compliance requirement - maximum aggregate maximum unhedged variable rate debt (percent)	30.00%
Compliance requirement - maximum payout ratio (percent)	95.00%
Restrictions - maximum unimproved land as percentage of total asset value (percent)	5.00%
Restrictions - pre-leased developments under development as a percentage of total asset value, maximum (percent)	20.00%
Restrictions - investments in unconsolidated affiliates as percentage of total asset value, maximum (percent)	10.00%
Restrictions - investments in mortgage notes receivable as percentage of total asset value, maximum (percent)	15.00%
Restrictions - leased assets under renovation as percentage of total asset value, maximum (percent)	10.00%
Restrictions - aggregate investment limitations as a percentage of total asset value, maximum (percent)	25.00%
Mortgages \| Pepsi Bottling Ventures Loan
Debt Instrument [Line Items]
Fixed interest rate	3.69%
Revolving Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Covenant - minimum pool properties \| property	15
Covenant -maximum pool value contributed by single pool property of tenant (percent)	15.00%
Covenant - maximum aggregate pool value to be contributed by pool properties subject to ground leases (percent)	15.00%
Covenant - maximum aggregate pool value to be contributed by pool properties under development (percent)	20.00%
Covenant - minimum aggregate leasing percentage (percent)	90.00%
Covenant - maximum unsecured leverage ratio (percent)	60.00%
Covenant - minimum unsecured interest coverage ratio	2.00
Pepsi Bottling Ventures \| Mortgages \| Pepsi Bottling Ventures Loan
Debt Instrument [Line Items]
Debt		$ 18,900
Fixed interest rate		3.69%