Debt Instrument, Basis Rate

No definition available.

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

- Definition

Debt Instrument, Extended Term

+ References

No definition available.

+ Details

Name:	gcnl_DebtInstrumentExtendedTerm
Namespace Prefix:	gcnl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Payment Terms, Duration Requiring Monthly Payments of Interest Only

+ References

No definition available.

+ Details

Name:	gcnl_DebtInstrumentPaymentTermsDurationRequiringMonthlyPaymentsofInterestOnly
Namespace Prefix:	gcnl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Term to Determine Contractual Interest Rate

+ References

No definition available.

+ Details

Name:	gcnl_DebtInstrumentTermtoDetermineContractualInterestRate
Namespace Prefix:	gcnl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Term to Determine Weighted Average Interest Rate

+ References

No definition available.

+ Details

Name:	gcnl_DebtInstrumentTermtoDetermineWeightedAverageInterestRate
Namespace Prefix:	gcnl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of extension under credit facility.

+ References

No definition available.

+ Details

Name:	gcnl_LineOfCreditFacilityExtensionTerm
Namespace Prefix:	gcnl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ 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)(1)
-URI http://asc.fasb.org/extlink&oid=109500613&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(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: 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=6877327&loc=d3e13212-122682

Reference 4: 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=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 3: 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=6877327&loc=d3e13212-122682

+ Details

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

- Definition

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

+ References

+ 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

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

+ Details

Name:	us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ 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 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

+ Details

Name:	us-gaap_DeferredFinanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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=109500613&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=6879938&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=6876686&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=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

+ References

+ Details

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

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
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_DebtInstrumentAxis=gcnl_KeyBankCreditFacilityMember
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:	us-gaap_LongtermDebtTypeAxis=us-gaap_MortgagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	dei_LegalEntityAxis=gcnl_GriffinCapitalEssentialAssetREITInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gcnl_UnsecuredCreditFacilityJuly2015Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=gcnl_Highway94MortgageLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=gcnl_InterestRateSwapOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Schedule of Debt (Details) - USD ($)						9 Months Ended	12 Months Ended
Debt - Schedule of Debt (Details) - USD ($)	Jun. 28, 2018	Mar. 31, 2018	Sep. 29, 2017	Oct. 22, 2015	Jul. 20, 2015	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016	Apr. 01, 2016	Feb. 25, 2016
Debt Instrument [Line Items]
Weighted average interest rate						3.81%	3.13%
Total principal						$ 490,055,000	$ 484,728,000	$ 460,428,000
Debt Issuance Costs, Net						(8,482,000)	(2,880,000)	(3,956,000)
Debt, net						$ 481,573,000	$ 481,848,000	456,472,000
LIBOR
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate						2.11%
Debt Instrument, Basis Rate							1.57%
Revolving Credit Facility \| Key Bank Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Term	4 years
Line Of Credit Facility, Extension Term	1 year
Line of Credit \| Key Bank Credit Facility [Member]
Debt Instrument [Line Items]
Weighted average interest rate							2.92%
Total principal						$ 85,000	$ 357,758,000	$ 333,458,000
Contractual stated interest rate (percent)							2.87%
Effective interest rate (percent)						3.65%	3.32%
Debt Instrument, Term						4 years	4 years	4 years
Line Of Credit Facility, Extension Term						1 year	1 year	1 year
Line of Credit \| Key Bank Credit Facility [Member] \| LIBOR
Debt Instrument [Line Items]
Debt Instrument, Term to Determine Weighted Average Interest Rate							365 days
Debt Instrument, Term to Determine Contractual Interest Rate							360 days
Spread over variable rate (percent)		1.50%				1.30%	1.50%
Mortgages
Debt Instrument [Line Items]
Total principal						$ 376,970,000	$ 126,970,000
Mortgages \| BofA / Key Bank Loan [Member]
Debt Instrument [Line Items]
Total principal						$ 250,000,000	0
Contractual stated interest rate (percent)						4.32%
Effective interest rate (percent)						4.36%
Mortgages \| AIG Loan
Debt Instrument [Line Items]
Total principal						$ 126,970,000	126,970,000
Contractual stated interest rate (percent)						4.15%
Effective interest rate (percent)						4.22%
Notes Payable, Other Payables [Member] \| AIG Loan
Debt Instrument [Line Items]
Total principal							$ 126,970,000	$ 126,970,000
Debt, net				$ 127,000,000
Contractual stated interest rate (percent)				4.15%			4.15%
Effective interest rate (percent)							4.22%
Debt Instrument, Term				10 years			10 years
Debt Instrument, Payment Terms, Duration Requiring Monthly Payments of Interest Only				5 years			5 years
Notes Payable, Other Payables [Member] \| Term Loan [Member]
Debt Instrument [Line Items]
Total principal						$ 113,000,000	$ 0
Effective interest rate (percent)						3.58%
Notes Payable, Other Payables [Member] \| Term Loan [Member] \| LIBOR
Debt Instrument [Line Items]
Spread over variable rate (percent)						1.25%
Griffin Capital Essential Asset REIT, Inc. [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount						$ 1,150,000,000
Total principal						1,363,776,000	1,397,779,000	1,458,343,000
Unamortized Deferred Financing Costs and Discounts, net						(9,426,000)	(11,695,000)	(10,808,000)
Debt Issuance Costs, Net							(11,414,000)
Debt, net						$ 1,354,350,000	$ 1,386,084,000	1,447,535,000
Griffin Capital Essential Asset REIT, Inc. [Member] \| LIBOR
Debt Instrument [Line Items]
Effective interest rate (percent)						2.11%	1.56%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Revolving Credit Facility \| Term Loan
Debt Instrument [Line Items]
Total principal						$ 715,000,000	$ 715,000,000	715,000,000
Effective interest rate (percent)						3.89%	3.19%
Debt Instrument, Term					4 years
Debt instrument extended term					1 year
Griffin Capital Essential Asset REIT, Inc. [Member] \| Revolving Credit Facility \| Term Loan \| LIBOR
Debt Instrument [Line Items]
Spread over variable rate (percent)							1.40%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Revolving Credit Facility \| Revolver Loan
Debt Instrument [Line Items]
Total principal						$ 0	$ 10,153,000	397,409,000
Effective interest rate (percent)						3.77%	3.79%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Revolving Credit Facility \| Revolver Loan \| LIBOR
Debt Instrument [Line Items]
Spread over variable rate (percent)							1.45%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Fixed and Variable Rate Debt
Debt Instrument [Line Items]
Weighted average interest rate						3.70%	3.53%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Mortgages
Debt Instrument [Line Items]
Total principal						$ 648,776,000	$ 672,626,000	345,934,000
Griffin Capital Essential Asset REIT, Inc. [Member] \| Mortgages \| Plainfield Mortgage Loan [Member]
Debt Instrument [Line Items]
Total principal							$ 0	18,932,000
Contractual stated interest rate (percent)							0.00%
Effective interest rate (percent)							0.00%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Mortgages \| TW Telecom Loan
Debt Instrument [Line Items]
Total principal						$ 0	$ 19,169,000	20,353,000
Effective interest rate (percent)						0.00%	4.04%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Mortgages \| TW Telecom Loan \| LIBOR
Debt Instrument [Line Items]
Spread over variable rate (percent)							2.45%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Mortgages \| Bank of America loan
Debt Instrument [Line Items]
Total principal						$ 21,340,000	$ 21,694,000	22,149,000
Contractual stated interest rate (percent)						4.18%	4.175%
Effective interest rate (percent)						4.60%	4.59%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Mortgages \| Midland Mortgage Loan
Debt Instrument [Line Items]
Total principal						$ 102,753,000	$ 104,197,000	105,600,000
Contractual stated interest rate (percent)						3.94%	3.94%
Effective interest rate (percent)						4.12%	4.08%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Mortgages \| Emporia Partners loan
Debt Instrument [Line Items]
Total principal						$ 2,662,000	$ 2,978,000	3,377,000
Contractual stated interest rate (percent)						5.88%	5.88%
Effective interest rate (percent)						5.96%	5.96%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Mortgages \| BofA loan
Debt Instrument [Line Items]
Total principal						$ 22,309,000	$ 22,961,000	23,786,000
Contractual stated interest rate (percent)						6.08%	6.08%
Effective interest rate (percent)						5.16%	5.22%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Mortgages \| Highway 94 loan
Debt Instrument [Line Items]
Total principal						$ 16,714,000	$ 17,352,000	18,175,000
Contractual stated interest rate (percent)						3.75%	3.75%
Effective interest rate (percent)						4.65%	4.63%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Mortgages \| Bank of America loan
Debt Instrument [Line Items]
Total principal						$ 375,000,000	$ 375,000,000	0
Contractual stated interest rate (percent)			3.77%			3.77%	3.77%
Effective interest rate (percent)						3.91%	3.90%
Debt Instrument, Term			10 years			10 years
Griffin Capital Essential Asset REIT, Inc. [Member] \| Mortgages \| AIG Loan
Debt Instrument [Line Items]
Total principal						$ 107,998,000	$ 109,275,000	110,640,000
Contractual stated interest rate (percent)						4.96%	4.96%
Effective interest rate (percent)						5.07%	5.07%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Mortgages \| Ace Hardware Mortgage Loan [Member]
Debt Instrument [Line Items]
Total principal							$ 0	$ 22,922,000
Contractual stated interest rate (percent)							0.00%
Spread over variable rate (percent)								5.00%
Effective interest rate (percent)							0.00%
Griffin Capital Essential Asset REIT, Inc. [Member] \| Fixed Rate Debt
Debt Instrument [Line Items]
Weighted average interest rate						3.75%	3.54%
Interest Rate Swap
Debt Instrument [Line Items]
Derivative, Notional Amount						$ 100,000,000	$ 200,000,000.0		$ 100,000,000	$ 100,000,000.0
Interest Rate Swap \| Griffin Capital Essential Asset REIT, Inc. [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount						$ 425,000,000	$ 725,000,000.0