Area of real estate that have been pledged as collateral for borrowings.

No definition available.

Name:	grif_AreaOfRealEstatePledgedAsCollateral
Namespace Prefix:	grif_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Fixed charge coverage ratio for line of credit facility.

+ References

No definition available.

+ Details

Name:	grif_LineOfCreditFacilityFixedCoverageRatio
Namespace Prefix:	grif_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of borrowing capacity that is unavailable to the borrower.

+ References

No definition available.

+ Details

Name:	grif_LineOfCreditFacilityHoldbackAmount
Namespace Prefix:	grif_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum liquidity requirement to be maintained under line of credit facility.

+ References

No definition available.

+ Details

Name:	grif_LineOfCreditFacilityMinimumLiquidityRequired
Namespace Prefix:	grif_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum percentage of loan to value.

+ References

No definition available.

+ Details

Name:	grif_MaximumPercentageOfLoanToValue
Namespace Prefix:	grif_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The maximum period with in which the entity has to get performance financing from the date of withdrawn from acquisition credit line.

+ References

No definition available.

+ Details

Name:	grif_MaximumPeriodForObtainingPermanentFinancingFromDrawnOfFundsFromAcquisitionCreditLine
Namespace Prefix:	grif_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum debt service coverage ratio.

+ References

No definition available.

+ Details

Name:	grif_MinimumDebtServiceCoverageRatio
Namespace Prefix:	grif_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of total debt plus certain equity components to total assets.

+ References

No definition available.

+ Details

Name:	grif_PercentageOfDebtAndEquityToAssets
Namespace Prefix:	grif_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of purchase price of real estate acquisitions.

+ References

No definition available.

+ Details

Name:	grif_PercentageOfPurchasePriceOfRealEstateAcquisitions
Namespace Prefix:	grif_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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

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

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

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the 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))
-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 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 3: 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=119400593&loc=d3e572229-122910

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

The lowest amount of net worth (total assets minus total liabilities) required by secondary market investors or state-imposed regulatory mandates.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)(a)
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47080-110998

+ Details

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

- Definition

Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3291-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=grif_GriffinCenterSouthBloomfieldCTMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=grif_GriffinCenterMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=grif_IndustrialOrWarehouseBuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

Revolving Credit Agreements (Details) $ in Thousands		1 Months Ended	6 Months Ended
Revolving Credit Agreements (Details) $ in Thousands	Jun. 01, 2020 USD ($)	Jun. 30, 2020 USD ($)	May 31, 2020 USD ($) ft²	Nov. 30, 2020 USD ($)	Sep. 19, 2019 ft²
Revolving credit agreement
Maximum percentage of loan to value			65.00%
Minimum debt service coverage ratio			1.25
Repayment of the credit line	$ 4,100
LIBOR
Revolving credit agreement
Variable interest rate margin (as a percent)		2.56%
Webster Credit Line
Revolving credit agreement
Maximum borrowing capacity			$ 19,500
Maximum percentage of loan to value			72.00%
Minimum liquidity			$ 5,000
Fixed charge coverage ratio			1.1
Standby letters of credit aggregate amount			$ 484
Outstanding borrowings under credit line			$ 0
Webster Credit Line \| Subsequent events
Revolving credit agreement
Holdback amount		$ 306
Webster Credit Line \| Griffin Center South, Bloomfield, CT
Revolving credit agreement
Area of collateralized properties (in square feet) \| ft²			235,000
Webster Credit Line \| Single-story office building in Griffin Center
Revolving credit agreement
Area of collateralized properties (in square feet) \| ft²			48,000
Webster Credit Line \| Industrial/warehouse building
Revolving credit agreement
Area of collateralized properties (in square feet) \| ft²					31,000
Webster Credit Line \| LIBOR
Revolving credit agreement
Variable interest rate margin (as a percent)			2.50%
Acquisition Credit Line
Revolving credit agreement
Maximum borrowing capacity			$ 15,000
Minimum liquidity			$ 5,000
Fixed charge coverage ratio			1.1
Purchase price of real estate acquisitions (as a percent)			65.00%
Maximum period for obtaining permanent finance from date of drawn			135 days
Minimum debt service coverage ratio			1.25
Minimum net worth			$ 80,000
Maximum percentage of total debt plus preferred stock to total assets allowed			50.00%
Outstanding borrowings under credit line			$ 4,100	$ 5,875
Weighted average interest rate			3.12%
Acquisition Credit Line \| LIBOR
Revolving credit agreement
Variable interest rate margin (as a percent)			2.75%