Mortgage Notes Payable, Net - Multi-Tenant Mortgage Loan V (Details) - KeyBank National Association - Multi-Tenant Mortgage Loan V - Mortgage notes payable $ in Millions	Sep. 12, 2019 USD ($) sate property
Debt Instrument [Line Items]
Proceeds from loans borrowed	$ 204.0
Collateral, number of leased offices and industrial properties \| property	12
Number of states in which mortgaged properties are located (state) \| sate	10
Repayments of debt	$ 86.5
Deposits into reserve accounts	0.3
Working capital and general corporate	$ 126.5
Interest rate	3.65%

Debt Instrument, Collateral, Number Of Leased Offices And Industrial Properties

No definition available.

Name:	gnl_DebtInstrumentCollateralNumberOfLeasedOfficesAndIndustrialProperties
Namespace Prefix:	gnl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Number Of States In Which Mortgaged Properties Are Located

+ References

No definition available.

+ Details

Name:	gnl_DebtInstrumentNumberOfStatesInWhichMortgagedPropertiesAreLocated
Namespace Prefix:	gnl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Deposits Into Reserve Accounts

+ References

No definition available.

+ Details

Name:	gnl_DepositsIntoReserveAccounts
Namespace Prefix:	gnl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

The maximum amount of borrowing capacity under a line of credit that is available as of the balance sheet date for financing purchases of goods acquired for inventory or imminent delivery to a customer.

+ References

No definition available.

+ Details

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

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585

+ Details

Name:	us-gaap_RepaymentsOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=gnl_KeyBankNationalAssociationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=gnl_MultiTenantMortgageLoanVMember
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: