Amount of loan modification requests received under a loan deferment program.

No definition available.

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- Definition

Number of loan modification requests received under a loan deferment program.

+ References

No definition available.

+ Details

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Namespace Prefix:	gcbc_
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- References

No definition available.

+ Details

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Period Type:	duration

- Definition

The term of deferral of principal and/or interest payments under a loan deferral program, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	gcbc_LoanDeferralProgramTermOfPaymentDeferral
Namespace Prefix:	gcbc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953682-111524

+ Details

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Period Type:	duration

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Loans and Allowance for Loan Losses, Troubled Debt Restructurings (Details) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) Loan Contract	Sep. 30, 2019 Contract	Jun. 30, 2020 USD ($) Loan
Troubled Debt Restructurings [Abstract]
TDR loans which have subsequently defaulted during the period \| Contract	0	0
Amount of loan modification requests received under loan deferment program \| $	$ 67.4		$ 193.5
Number of loan modification requests received under loan deferment program \| Loan	201		706
Minimum [Member]
Troubled Debt Restructurings [Abstract]
Term of payment deferral under loan deferment program			3 months
Maximum [Member]
Troubled Debt Restructurings [Abstract]
Term of payment deferral under loan deferment program			6 months